257 results on '"Peter Saalfrank"'
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2. Manipulating tunnelling gateways in condensed phase isomerization
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Arnab Choudhury, Shreya Sinha, David Harlander, Jessalyn DeVine, Alexander Kandratsenka, Peter Saalfrank, Dirk Schwarzer, and Alec M. Wodtke
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astrochemistry ,gateway tunneling ,isomerization ,tunneling ,Science - Abstract
Abstract When a chemical reaction occurs via tunnelling, a simple mass‐dependence is expected, where substitution of atoms by heavier isotopes leads to a reduced reaction rate. However, as shown in a recent study of CO orientational isomerization at the NaCl(1 0 0) interface, the lightest isotopologues need not exhibit the fastest tunnelling; for the CO/NaCl system, the non‐monotonic mass‐dependence is understood through a new picture of condensed phase tunnelling where the overall rate is dominated by a few pairs of reactant/product states. These state‐pairs – termed quantum gateways – gain dynamical importance through accidentally enhanced tunnelling probabilities, facilitated by a confluence of the energetic landscape underlying the reaction as well as the phonon bath of the surrounding medium. Here, we explore gateway tunnelling through measurements of the kinetic isotope effect for CO isomerization in a monolayer buried by many layers of either CO or N2. With an N2 overlayer, tunnelling rates are accelerated for all four isotopologues (12C16O, 13C16O, 12C18O and 13C18O), but the degree of acceleration is isotopologue‐specific and non‐intuitively mass dependent. A one‐dimensional tunnelling model involving an Eckart barrier cannot capture this behaviour. This reflects how a modification of the potential energy surface moves states in and out of resonance, thereby changing which tunnelling gateways can be accessed in the isomerization reaction. Key points The paper describes new systems that showcase resonance‐enhanced condensed phase tunnelling. Condensed phase tunnelling as described in this work may have implications for astrochemistry. A previously hypothesized mechanism is subjected to subsequent experimental scrutiny – the hypothesis stands the test.
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- 2023
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3. Raman Enhancement of Nanoparticle Dimers Self-Assembled Using DNA Origami Nanotriangles
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Sergio Kogikoski, Kosti Tapio, Robert Edler von Zander, Peter Saalfrank, and Ilko Bald
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surface-enhanced Raman scattering ,DNA origami ,resonance Raman scattering ,nanoparticle dimers ,Organic chemistry ,QD241-441 - Abstract
Surface-enhanced Raman scattering is a powerful approach to detect molecules at very low concentrations, even up to the single-molecule level. One important aspect of the materials used in such a technique is how much the signal is intensified, quantified by the enhancement factor (EF). Herein we obtained the EFs for gold nanoparticle dimers of 60 and 80 nm diameter, respectively, self-assembled using DNA origami nanotriangles. Cy5 and TAMRA were used as surface-enhanced Raman scattering (SERS) probes, which enable the observation of individual nanoparticles and dimers. EF distributions are determined at four distinct wavelengths based on the measurements of around 1000 individual dimer structures. The obtained results show that the EFs for the dimeric assemblies follow a log-normal distribution and are in the range of 106 at 633 nm and that the contribution of the molecular resonance effect to the EF is around 2, also showing that the plasmonic resonance is the main source of the observed signal. To support our studies, FDTD simulations of the nanoparticle’s electromagnetic field enhancement has been carried out, as well as calculations of the resonance Raman spectra of the dyes using DFT. We observe a very close agreement between the experimental EF distribution and the simulated values.
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- 2021
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4. Band gap engineering in two-dimensional materials by functionalization: Methylation of graphene and graphene bilayers
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Elham Mazarei, Christopher Penschke, and Peter Saalfrank
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Graphene is well known for its unique combination of electrical and mechanical properties. However, its vanishing band gap limits the use of graphene in microelectronics. Covalent functionalization of graphene has been a common approach to address this critical issue and introduce a band gap. In this paper, we systematically analyze the functionalization of single-layer graphene (SLG) and bilayer graphene (BLG) with methyl (CH3), using periodic density functional theory (DFT) at the PBE+D3 level of theory. We also include a comparison of methylated single-layer and bilayer graphene, as well as a discussion of different methylation options (radicalic, cationic and anionic). For SLG, methyl coverages ranging from 1/8 to 1/1, (i.e., the fully methylated analog of graphane) are considered. We find that up to a coverage θ of 1/2, graphene readily accepts CH3, with neighbour CH3 groups prefering trans positions. Above θ = 1/2, the tendency to accept further CH3 weakens and the lattice constant increases. The band gap behaves less regular, but overall, it increases with increasing methyl coverage. Thus, methylated graphene shows potential for developing band gap-tuned microelectronics devices and may offer further functionalization options. To guide in the interpretation of methylation experiments, vibrational signatures of various species are characterized by normal mode analysis (NMA), their vibrational density of states (VDOS), and infrared (IR) spectra, the latter two obtained from ab initio molecular dynamics (AIMD) in combination with a velocity-velocity autocorrelation function (VVAF) approach.
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- 2023
5. Femtosecond laser-induced desorption of hydrogen molecules from Ru(0001): A systematic study based on machine-learned potentials
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Steven Lindner, Ivor Lončarić, Lovro Vrček, Maite Alducin, J. I. Juaristi, and Peter Saalfrank
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Femtosecond laser-induced dynamics of molecules on metal surfaces can be seamlessly simulated with all nuclear degrees of freedom using ab-initio molecular dynamics with electronic friction (AIMDEF) and stochastic forces which are a function of a time-dependent electronic temperature. This has recently been demonstrated for hot-electron mediated desorption of hydrogen molecules from a Ru(0001) surface covered with H and D atoms [Juaristi et al., Phys. Rev. B 2017, 95, 125439]. Unfortunately, AIMDEF simulations come with a very large computational expense that severely limits statistics and propagation times. To keep ab-initio accuracy and allow for better statistical sampling, we have developed a neural network interatomic potential of hydrogen on the Ru(0001) surface based on data from ab-initio molecular dynamics simulations of recombinative desorption. Using this potential we simulated femtosecond laser-induced recombinative desorption using varying unit cells, coverages, laser fluences, and isotope ratios with reliable statistics. As a result, we can systematically study a wide range of these parameters and follow dynamics over longer times than hitherto possible, demonstrating that our methodology is a promising way to realistically simulate femtosecond laser-induced dynamics of molecules on metals. Moreover, we show that previously used cell sizes and propagation times were too small to obtain converged results.
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- 2023
6. Structure and Reactivity of α-Al2O3(0001) Surfaces: How Do Al–I and Gibbsite-like Terminations Interconvert?
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Yanhua Yue, Giacomo Melani, Harald Kirsch, Alexander Paarmann, Peter Saalfrank, R. Kramer Campen, and Yujin Tong
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General Energy ,Chemie ,Physik (inkl. Astronomie) ,Physical and Theoretical Chemistry ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
The α-Al2O3(0001) surface has been extensively studied because of its significance in both fundamental research and application. Prior work suggests that in ultra-high-vacuum (UHV), in the absence of water, the so-called Al–I termination is thermodynamically favored, while in ambient, in contact with liquid water, a Gibbsite-like layer is created. While the view of the α-Al2O3(0001)/H2O(l) interface appears relatively clear in theory, experimental characterization of this system has resulted in estimates of surface acidity, i.e., isoelectric points, that differ by 4 pH units and surface structure that in some reports has non-hydrogen-bonded surface aluminol (Al–OH) groups and in others does not. In this study, we employed vibrational sum frequency spectroscopy (VSFS) and density functional theory (DFT) simulation to study the surface phonon modes of the differently terminated α-Al2O3(0001) surfaces in both UHV and ambient. We find that, on either water dosing of the Al–I in UHV or heat-induced dehydroxylation of the Gibbsite-like in ambient, the surfaces do not interconvert. This observation offers a new explanation for disagreements in prior work on the α-Al2O3(0001)/liquid water interface─different preparation methods may create surfaces that do not interconvert─and shows that the surface phonon spectral response offers a novel probe of interfacial hydrogen bonding structure.
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- 2022
7. Structural, electronic and vibrational properties of methylated single- and bilayer graphene: A density functional theory study
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Elham Mazarei, Christopher Penschke, and Peter Saalfrank
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The functionalization of graphene has an immediate effect on its chemical and physical properties. In this paper we systematically study the functionalization of single layer graphene (SLG) with methyl (CH3) radicals, using periodic density functional theory (DFT) at the PBE+D3 level of theory. Special emphasis is on identifying most stable structures and corresponding electronic properties (band gap, electronic density of states, spin polarization) as a function of methyl load. For SLG, methyl coverages ranging from 1/8 to 1/1 (i.e., the fully methylated analog of graphane) are considered. We find that up to a coverage of 1/2, graphene readily accepts CH3, with neighbour CH3 groups prefering trans positions, and band gaps increasing non-monotonically with methyl load. Above coverages of 1/2, the tendency to accept further CH3 weakens, lattice constants widen and the band gap behaves less regular. Besides radicalic methylation, we also study heterolytic methylation by either the methyl anion CH3- (reaction with CH3Li) or the methyl cation CH3+ (reaction with CH3Cl), with counterions also included. Finally, we consider methylation (with CH3 radicals) of bilayer graphene (BLG). To guide in the interpretation of methylation experiments, vibrational signatures of various species are characterized by normal mode analysis (NMA), their vibrational density of states (VDOS), and infrared (IR) spectra, the latter two obtained from ab initio molecular dynamics (AIMD).
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- 2023
8. Water on porous, nitrogen-containing layered carbon materials: the performance of computational model chemistries
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Christopher Penschke, Robert Edler von Zander, Alkit Beqiraj, Anna Zehle, Nicolas Jahn, Rainer Neumann, and Peter Saalfrank
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General Physics and Astronomy ,Physical and Theoretical Chemistry - Abstract
The performance of various computational model chemistries in predicting structural, thermodynamic and optical properties of water-covered carbon and nitrogen containing porous materials is investigated.
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- 2022
9. Cavity-Catalyzed Hydrogen Transfer Dynamics in an Entangled Molecular Ensemble under Vibrational Strong Coupling
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Eric W. Fischer and Peter Saalfrank
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Chemical Physics (physics.chem-ph) ,Quantum Physics ,Physics - Chemical Physics ,General Physics and Astronomy ,FOS: Physical sciences ,Physical and Theoretical Chemistry ,Quantum Physics (quant-ph) - Abstract
Microcavities have been shown to influence the reactivity of molecular ensembles by strong coupling of molecular vibrations to quantized cavity modes. In quantum mechanical treatments of such scenarios, frequently idealized models with single molecules and scaled, effective molecule-cavity interactions or alternatively ensemble models with simplified model Hamiltonians are used. In this work, we go beyond these models by applying an ensemble variant of the Pauli-Fierz Hamiltonian for vibro-polaritonic chemistry and numerically solve the underlying time-dependent Schr\"odinger equation to study the cavity-induced quantum dynamics in an ensemble of thioacetylacetone (TAA) molecules undergoing hydrogen transfer under vibrational strong coupling (VSC) conditions. Beginning with a single molecule coupled to a single cavity mode, we show that the cavity indeed enforces hydrogen transfer from an enol to an enethiol configuration with transfer rates significantly increasing with light-matter interaction strength. This positive effect of the cavity on reaction rates is different from several other systems studied so far, where a retarding effect of the cavity on rates was found. It is argued that the cavity ``catalyzes'' the reaction by transfer of virtual photons to the molecule. The same concept applies to ensembles with up to $N=20$ TAA molecules coupled to a single cavity mode, where an additional, significant, ensemble-induced collective isomerization rate enhancement is found. The latter is traced back to complex entanglement dynamics of the ensemble, which we quantify by means of von Neumann-entropies. A non-trivial dependence of the dynamics on ensemble size is found, clearly beyond scaled single-molecule models, which we interpret as transition from a multi-mode Rabi to a system-bath-type regime as $N$ increases., Comment: Manuscript 9 pages, 5 figures (minor changes in v2). Supplementary Information 7 pages, 5 figures (Section III rewritten in v2 after peer-review)
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- 2023
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10. Programmable Photocatalytic Activity of Multicomponent Covalent Organic Frameworks Used as Metallaphotocatalysts
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Michael Traxler, Susanne Reischauer, Sarah Vogl, Jérôme Roeser, Jabor Rabeah, Christopher Penschke, Peter Saalfrank, Bartholomäus Pieber, and Arne Thomas
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540 Chemie und zugeordnete Wissenschaften ,catalysis ,tuneable activity ,Organic Chemistry ,cross-coupling ,General Chemistry ,covalent organic frameworks ,500 Naturwissenschaften und Mathematik::540 Chemie::540 Chemie und zugeordnete Wissenschaften ,photoredox - Abstract
The multicomponent approach allows to incorporate several functionalities into a single covalent organic framework (COF) and consequently allows the construction of bifunctional materials for cooperative catalysis. The well-defined structure of such multicomponent COFs is furthermore ideally suited for structure-activity relationship studies. We report a series of multicomponent COFs that contain acridine- and 2,2’-bipyridine linkers connected through 1,3,5-benzenetrialdehyde derivatives. The acridine motif is responsible for broad light absorption, while the bipyridine unit enables complexation of nickel catalysts. These features enable the usage of the framework materials as catalysts for light-mediated carbon−heteroatom cross-couplings. Variation of the node units shows that the catalytic activity correlates to the keto-enamine tautomer isomerism. This allows switching between high charge-carrier mobility and persistent, localized charge-separated species depending on the nodes, a tool to tailor the materials for specific reactions. Moreover, nickel-loaded COFs are recyclable and catalyze cross-couplings even using red light irradiation.
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- 2023
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11. Gaussian-Type Orbital Calculations for High Harmonic Generation in Vibrating Molecules: Benchmarks for H2+
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Guennaddi K. Paramonov, Tillmann Klamroth, Christoph Witzorky, Foudhil Bouakline, Peter Saalfrank, and Ralph Jaquet
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Physics ,Attosecond ,Configuration interaction ,Dihydrogen cation ,Computer Science Applications ,Schrödinger equation ,Computational physics ,symbols.namesake ,Harmonics ,Ionization ,symbols ,High harmonic generation ,Physical and Theoretical Chemistry ,Wave function - Abstract
The response of the hydrogen molecular ion, H2+, to few-cycle laser pulses of different intensities is simulated. To treat the coupled electron-nuclear motion, we use adiabatic potentials computed with Gaussian-type basis sets together with a heuristic ionization model for the electron and a grid representation for the nuclei. Using this mixed-basis approach, the time-dependent Schrodinger equation is solved, either within the Born-Oppenheimer approximation or with nonadiabatic couplings included. The dipole response spectra are compared to all-grid-based solutions for the three-body problem, which we take as a reference to benchmark the Gaussian-type basis set approaches. Also, calculations employing the fixed-nuclei approximation are performed, to quantify effects due to nuclear motion. For low intensities and small ionization probabilities, we get excellent agreement of the dynamics using Gaussian-type basis sets with the all-grid solutions. Our investigations suggest that high harmonic generation (HHG) and high-frequency response, in general, can be reliably modeled using Gaussian-type basis sets for the electrons for not too high harmonics. Further, nuclear motion destroys electronic coherences in the response spectra even on the time scale of about 30 fs and affects HHG intensities, which reflect the electron dynamics occurring on the attosecond time scale. For the present system, non-Born-Oppenheimer effects are small. The Gaussian-based, nonadiabatically coupled, time-dependent multisurface approach to treat quantum electron-nuclear motion beyond the non-Born-Oppenheimer approximation can be easily extended to approximate wavefunction methods, such as time-dependent configuration interaction singles (TD-CIS), for systems where no benchmarks are available.
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- 2021
12. Photoisomerization of an Azobenzene‐Containing Surfactant Within a Micelle
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Evgenii Titov, Peter Saalfrank, Anjali Sharma, Svetlana Santer, Marek Bekir, and Nino Lomadze
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Materials science ,Photoisomerization ,Organic Chemistry ,Institut für Physik und Astronomie ,Surface hopping ,Photochemistry ,Micelle ,Analytical Chemistry ,chemistry.chemical_compound ,Reaction rate constant ,Azobenzene ,chemistry ,Pulmonary surfactant ,ddc:540 ,Institut für Chemie ,Physical and Theoretical Chemistry - Abstract
Photosensitive azobenzene-containing surfactants have attracted great attention in past years because they offer a means to control soft-matter transformations with light. At concentrations higher than the critical micelle concentration (CMC), the surfactant molecules aggregate and form micelles, which leads to a slowdown of the photoinduced trans -> cis azobenzene isomerization. Here, we combine nonadiabatic dynamics simulations for the surfactant molecules embedded in the micelles with absorption spectroscopy measurements of micellar solutions to uncover the reasons responsible for the reaction slowdown. Our simulations reveal a decrease of isomerization quantum yields for molecules inside the micelles. We also observe a reduction of extinction coefficients upon micellization. These findings explain the deceleration of the trans -> cis switching in micelles of the azobenzene-containing surfactants.
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- 2021
13. Protonated Imine‐Linked Covalent Organic Frameworks for Photocatalytic Hydrogen Evolution
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Martin Oschatz, Sol Youk, Meng-Yang Ye, Roel van de Krol, Christopher Penschke, Amitava Acharjya, Reinhard Schomäcker, Zdravko Kochovski, Shuang Li, Peter Saalfrank, Tianyi Wang, Jabor Rabeah, Arne Thomas, Julia Grüneberg, Michael Schwarze, Yan Lu, Jérôme Roeser, and Jin Yang
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Photocatalysis | Hot Paper ,Hydrogen ,Chemistry ,protonation ,Visible light irradiation ,Imine ,chemistry.chemical_element ,Protonation ,General Medicine ,General Chemistry ,Photochemistry ,Catalysis ,Organic semiconductor ,chemistry.chemical_compound ,Covalent bond ,imines ,Photocatalysis ,Chemical Energy Carriers ,photocatalytic hydrogen evolution ,Hydrogen evolution ,500 Naturwissenschaften und Mathematik::540 Chemie::540 Chemie und zugeordnete Wissenschaften ,covalent organic frameworks ,Research Articles ,Research Article - Abstract
Covalent organic frameworks (COFs) have emerged as an important class of organic semiconductors and photocatalysts for the hydrogen evolution reaction (HER)from water. To optimize their photocatalytic activity, typically the organic moieties constituting the frameworks are considered and the most suitable combinations of them are searched for. However, the effect of the covalent linkage between these moieties on the photocatalytic performance has rarely been studied. Herein, we demonstrate that donor‐acceptor (D‐A) type imine‐linked COFs can produce hydrogen with a rate as high as 20.7 mmol g−1 h−1 under visible light irradiation, upon protonation of their imine linkages. A significant red‐shift in light absorbance, largely improved charge separation efficiency, and an increase in hydrophilicity triggered by protonation of the Schiff‐base moieties in the imine‐linked COFs, are responsible for the improved photocatalytic performance., Protonation of imine‐linked COFs yields significant variations of their (opto)electronic properties and results in a largely enhanced performance in photocatalytic hydrogen evolution from water. This is attributed to an enhanced light absorption ability, charge separation efficiency, and hydrophilicity of imine‐linked COFs upon protonation.
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- 2021
14. Hydration at highly crowded interfaces
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Christopher Penschke, John Thomas, Cord Bertram, Angelos Michaelides, Karina Morgenstern, Peter Saalfrank, and Uwe Bovensiepen
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Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Physics and Astronomy ,Physik (inkl. Astronomie) - Abstract
Understanding the molecular and electronic structure of electrolytes at interfaces requires an analysis of the interactions between the electrode surface, the ions, and the solvent environment on equal footing. Here, we tackle this challenge by exploring the initial stages of Cs+ hydration on a Cu(111) surface by combining experiment and theory. Remarkably, we observe "inside out" solvation of Cs ions, i.e, their preferential location at the perimeter of the water clusters on the metal surface. In addition, water-Cs complexes containing multiple Cs+ ions are observed to form at these surfaces. Established models based on maximum ion-water coordination and the double layer notion cannot account for this situation and the complex interplay of microscopic interactions is the key to a fundamental understanding., 5 pages, 3 figures
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- 2022
15. Cavity-induced Non-Adiabatic Dynamics and Spectroscopy of Molecular Rovibrational Polaritons studied by Multi-Mode Quantum Models
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Eric W. Fischer and Peter Saalfrank
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Chemical Physics (physics.chem-ph) ,Physics - Chemical Physics ,ddc:540 ,General Physics and Astronomy ,Institut für Physik und Astronomie ,FOS: Physical sciences ,Physics::Optics ,Physical and Theoretical Chemistry ,Optics (physics.optics) ,Physics - Optics - Abstract
We study theoretically the quantum dynamics and spectroscopy of rovibrational polaritons formed in a model system composed of a single rovibrating diatomic molecule, which interacts with two degenerate, orthogonally polarized modes of an optical Fabry-P\'erot cavity. We employ an effective rovibrational Pauli-Fierz Hamiltonian in length gauge representation and identify three-state vibro-polaritonic conical intersections (VPCIs) between singly-excited vibro-polaritonic states in a two-dimensional angular coordinate branching space. The lower and upper vibrational polaritons are of mixed light-matter hybrid character, whereas the intermediate state is purely photonic in nature. The VPCIs provide effective population transfer channels between singly-excited vibrational polaritons, which manifest in rich interference patterns in rotational densities. Spectroscopically, three bright singly-excited states are identified, when an external infrared laser field couples to both a molecular and a cavity mode. The non-trivial VPCI topology manifests as pronounced multi-peak progression in the spectral region of the upper vibrational polariton, which is traced back to the emergence of rovibro-polaritonic light-matter hybrid states. Experimentally ubiquitous spontaneous emission from cavity modes induces a dissipative reduction of intensity and peak broadening, which mainly influences the purely photonic intermediate state peak as well as the rovibro-polaritonic progression., Comment: 14 pages, 7 figures; accepted at Journal of Chemical Physics
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- 2022
16. 'Inverted' CO molecules on NaCl(100): a quantum mechanical study
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Peter Saalfrank and Shreya Sinha
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Physics ,Anharmonicity ,Degenerate energy levels ,General Physics and Astronomy ,Potential energy ,Schrödinger equation ,Transition state theory ,symbols.namesake ,symbols ,Physical and Theoretical Chemistry ,Atomic physics ,Isomerization ,Quantum ,Excitation - Abstract
Somewhat surprisingly, inverted ("O-down") CO adsorbates on NaCl(100) were recently observed experimentally after infrared vibrational excitation (Lau et al., Science, 2020, 367, 175-178). Here we characterize these species using periodic density functional theory and a quantum mechanical description of vibrations. We determine stationary points and minimum energy paths for CO inversion, for low (1/8 and 1/4 monolayers (ML)) and high (1 ML) coverages. Transition state theory is applied to estimate thermal rates for "C-down" to "O-down" isomerization and the reverse process. For the 1/4 ML p(1 × 1) structure, two-dimensional and three-dimensional potential energy surfaces and corresponding anharmonic vibrational eigenstates obtained from the time-independent nuclear Schrodinger equation are presented. We find (i) rather coverage-independent CO inversion energies (of about 0.08 eV or 8 kJ mol-1 per CO) and corresponding classical activation energies for "C-down" to "O-down" isomerization (of about 0.15 eV or 14 kJ mol-1 per CO); (ii) thermal isomerization rates at 22 K which are vanishingly small for the "C-down" to "O-down" isomerization but non-negligible for the back reaction; (iii) several "accidentally degenerate" pairs of eigenstates well below the barrier, each pair describing "C-down" to "O-down" localized states.
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- 2021
17. Vibrational energy relaxation of interfacial OH on a water-covered α-Al2O3(0001) surface: a non-equilibrium ab initio molecular dynamics study
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Yuki Nagata, Giacomo Melani, and Peter Saalfrank
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Materials science ,Phonon ,General Physics and Astronomy ,Infrared spectroscopy ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Chemical physics ,Excited state ,Dissipative system ,Vibrational energy relaxation ,Molecule ,Relaxation (physics) ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,0210 nano-technology ,Spectroscopy - Abstract
Vibrational relaxation of adsorbates is a sensitive tool to probe energy transfer at gas/solid and liquid/solid interfaces. The most direct way to study relaxation dynamics uses time-resolved spectroscopy. Here we report on a non-equilibrium ab initio molecular dynamics (NE-AIMD) methodology to model vibrational relaxation of OH vibrations on a hydroxylated, water-covered α-Al2O3(0001) surface. In our NE-AIMD approach, after exciting selected O–H bonds their coupling to surface phonons and to the water adlayer is analyzed in detail, by following both the energy flow in time, as well as the time-evolution of Vibrational Density of States (VDOS) curves. The latter are obtained from Time-dependent Correlation Functions (TCFs) and serve as prototypical, generic representatives of time-resolved vibrational spectra. As most important results, (i) we find a few-picosecond lifetime of the excited modes and (ii) identify both hydrogen-bonded aluminols and water molecules in the adsorbed water layer as main dissipative channels, while the direct coupling to Al2O3 surface phonons is of minor importance on the timescales of interest. Our NE-AIMD/TCF methodology is powerful for complex adsorbate systems, in principle even reacting ones, and opens a way towards time-resolved vibrational spectroscopy.
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- 2021
18. Many-electron dynamics in laser-driven molecules: wavefunction theory vs. density functional theory
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Tillmann Klamroth, Florian Bedurke, and Peter Saalfrank
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Physics ,Dipole ,Atomic orbital ,Harmonics ,Physics::Atomic and Molecular Clusters ,General Physics and Astronomy ,High harmonic generation ,Density functional theory ,Physical and Theoretical Chemistry ,Configuration interaction ,Atomic physics ,Population inversion ,Wave function - Abstract
With recent experimental advances in laser-driven electron dynamics in polyatomic molecules, the need arises for their reliable theoretical modelling. Among efficient, yet fairly accurate methods for many-electron dynamics are Time-Dependent Configuration Interaction Singles (TD-CIS) (a Wave Function Theory (WFT) method), and Real-Time Time-Dependent Density Functional Theory (RT-TD-DFT), respectively. Here we compare TD-CIS combined with extended Atomic Orbital (AO) bases, TD-CIS/AO, with RT-TD-DFT in a grid representation of the Kohn–Sham orbitals, RT-TD-DFT/Grid. Possible ionization losses are treated by complex absorbing potentials in energy space (for TD-CIS/AO) or real space (for RT-TD-DFT), respectively. The comparison is made for two test cases: (i) state-to-state transitions using resonant lasers (π-pulses), i.e., bound electron motion, and (ii) large-amplitude electron motion leading to High Harmonic Generation (HHG). Test systems are a H2 molecule and cis- and trans-1,2-dichlorethene, C2H2Cl2, (DCE). From time-dependent electronic energies, dipole moments and from HHG spectra, the following observations are made: first, for bound state-to-state transitions enforced by π-pulses, TD-CIS nicely accounts for the expected population inversion in contrast to RT-TD-DFT, in agreement with earlier findings. Secondly, when using laser pulses under non-resonant conditions, dipole moments and lower harmonics in HHG spectra are obtained by TD-CIS/AO which are in good agreement with those obtained with RT-TD-DFT/Grid. Deviations become larger for higher harmonics and at low laser intensities, i.e., for low-intensity HHG signals. We also carefully test effects of basis sets for TD-CIS/AO and grid size for RT-TD-DFT/Grid, different exchange–correlation functionals in RT-TD-DFT, and absorbing boundaries. Finally, for the present examples, TD-CIS/AO is observed to be at least an order of magnitude more computationally efficient than RT-TD-DFT/Grid.
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- 2021
19. Cavity-altered thermal isomerization rates and dynamical resonant localization in vibro-polaritonic chemistry
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Eric W. Fischer, Janet Anders, and Peter Saalfrank
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Chemical Physics (physics.chem-ph) ,Quantum Physics ,Physics - Chemical Physics ,General Physics and Astronomy ,FOS: Physical sciences ,Physical and Theoretical Chemistry ,Quantum Physics (quant-ph) - Abstract
It has been experimentally demonstrated that reaction rates for molecules embedded in microfluidic optical cavities are altered when compared to rates observed under "ordinary" reaction conditions. However, precise mechanisms of how strong coupling of an optical cavity mode to molecular vibrations affect the reactivity and how resonance behavior emerges are still under dispute. In the present work, we approach these mechanistic issues from the perspective of a thermal model reaction, the inversion of ammonia along the umbrella mode, in presence of a single cavity mode of varying frequency and coupling strength. A topological analysis of the related cavity Born-Oppenheimer potential energy surface in combination with quantum mechanical and transition state theory rate calculations reveals two quantum effects, leading to decelerated reaction rates in qualitative agreement with experiments: The stiffening of quantized modes perpendicular to the reaction path at the transition state, which reduces the number of thermally accessible reaction channels, and the broadening of the barrier region which attenuates tunneling. We find these two effects to be very robust in a fluctuating environment, causing statistical variations of potential parameters such as the barrier height. Further, by solving the time-dependent Schr\"odinger equation in the vibrational strong coupling regime, we identify a resonance behavior, in qualitative agreement with experimental and earlier theoretical work. The latter manifests as reduced reaction probability, when the cavity frequency $\omega_c$ is tuned resonant to a molecular reactant frequency. We find this effect to be based on the dynamical localization of the vibro-polaritonic wavepacket in the reactant well., Comment: 37 pages, 7 figures, some corrections added
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- 2022
20. A Dual pH‐ and Light‐Responsive Spiropyran‐Based Surfactant: Investigations on Its Switching Behavior and Remote Control over Emulsion Stability
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Martin Reifarth, Marek Bekir, Alain M. Bapolisi, Evgenii Titov, Fabian Nußhardt, Julius Nowaczyk, Dmitry Grigoriev, Anjali Sharma, Peter Saalfrank, Svetlana Santer, Matthias Hartlieb, and Alexander Böker
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General Chemistry ,Catalysis - Abstract
A cationic surfactant containing a spiropyran unit is prepared exhibiting a dual-responsive adjustability of its surface-active characteristics. The switching mechanism of the system relies on the reversible conversion of the non-ionic spiropyran (SP) to a zwitterionic merocyanine (MC) and can be controlled by adjusting the pH value and via light, resulting in a pH-dependent photoactivity: While the compound possesses a pronounced difference in surface activity between both forms under acidic conditions, this behavior is suppressed at a neutral pH level. The underlying switching processes are investigated in detail, and a thermodynamic explanation based on a combination of theoretical and experimental results is provided. This complex stimuli-responsive behavior enables remote-control of colloidal systems. To demonstrate its applicability, the surfactant is utilized for the pH-dependent manipulation of oil-in-water emulsions.
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- 2022
21. Ein dual‐responsives pH‐ und lichtschaltbares Tensid mit einer Spiropyran‐Einheit: Untersuchungen zum Schaltmechanismus und Anwendung zur Steuerung von Emulsionsstabilitäten
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Martin Reifarth, Marek Bekir, Alain M. Bapolisi, Evgenii Titov, Fabian Nußhardt, Julius Nowaczyk, Dmitry Grigoriev, Anjali Sharma, Peter Saalfrank, Svetlana Santer, Matthias Hartlieb, and Alexander Böker
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General Medicine - Published
- 2022
22. Reaction barriers on non-conducting surfaces beyond periodic local MP2: Diffusion of hydrogen on α-Al
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Thomas, Mullan, Lorenzo, Maschio, Peter, Saalfrank, and Denis, Usvyat
- Abstract
The quest for "chemical accuracy" is becoming more and more demanded in the field of structure and kinetics of molecules at solid surfaces. In this paper, as an example, we focus on the barrier for hydrogen diffusion on a α-Al
- Published
- 2022
23. BLUF Hydrogen network dynamics and UV/Vis spectra: A combined molecular dynamics and quantum chemical study.
- Author
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Jan P. Götze, Claudio Greco 0003, Roland Mitric, Vlasta Bonacic-Koutecký, and Peter Saalfrank
- Published
- 2012
- Full Text
- View/download PDF
24. Towards low-energy-light-driven bistable photoswitches : ortho-fluoroaminoazobenzenes
- Author
-
Evgenii Titov, Peter Saalfrank, Zafar Ahmed, Elina Kalenius, Arri Priimagi, Kim Kuntze, Jani Viljakka, Tampere University, and Materials Science and Environmental Engineering
- Subjects
aromaattiset yhdisteet ,Materials science ,photochemistry ,Bistability ,Light ,business.industry ,010405 organic chemistry ,116 Chemical sciences ,010402 general chemistry ,01 natural sciences ,fluori ,0104 chemical sciences ,Low energy ,Isomerism ,Light driven ,Optoelectronics ,valokemia ,Physical and Theoretical Chemistry ,business - Abstract
Thermally stable photoswitches that are driven with low-energy light are rare, yet crucial for extending the applicability of photoresponsive molecules and materials towards, e.g., living systems. Combined ortho-fluorination and -amination couples high visible light absorptivity of o-aminoazobenzenes with the extraordinary bistability of o-fluoroazobenzenes. Herein, we report a library of easily accessible o-aminofluoroazobenzenes and establish structure–property relationships regarding spectral qualities, visible light isomerization efficiency and thermal stability of the cis-isomer with respect to the degree of o-substitution and choice of amino substituent. We rationalize the experimental results with quantum chemical calculations, revealing the nature of low-lying excited states and providing insight into thermal isomerization. The synthesized azobenzenes absorb at up to 600 nm and their thermal cis-lifetimes range from milliseconds to months. The most unique example can be driven from trans to cis with any wavelength from UV up to 595 nm, while still exhibiting a thermal cis-lifetime of 81 days. Graphical abstract
- Published
- 2022
25. Reaction barriers on non-conducting surfaces beyond periodic local MP2: Diffusion of hydrogen on α-Al2O3(0001) as a test case
- Author
-
Thomas Mullan, Lorenzo Maschio, Peter Saalfrank, and Denis Usvyat
- Subjects
General Physics and Astronomy ,Physical and Theoretical Chemistry - Published
- 2022
26. Condensed phase isomerization through tunneling gateways
- Author
-
Alec Wodtke, Arnab Choudhury, Jessalyn DeVine, Shreya Sinha, Jascha Lau, Alexander Kandratsenka, Dirk Schwarzer, and Peter Saalfrank
- Subjects
Physics::Atomic and Molecular Clusters ,Physics::Chemical Physics - Abstract
We observe that the orientational isomerization of CO on a NaCl(100) surface proceeds by thermally-activated tunneling between 19 and 24K. The rate constants of three isotopomers follow an Arrhenius temperature dependence, exhibiting activation energies below the reaction’s predicted barrier height and anomalously small prefactors. In addition, the rates depend strongly on isotope, but non-intuitively on mass. A quantum rate theory of condensed-phase tunneling qualitatively explains these observations. Vibrationally excited states, accidentally close in energy but localized on opposite sides of the isomerization barrier, provide tunneling gateways between the isomers in a process that can be many orders-of-magnitude faster than rates predicted by commonly used semi-classical models. This suggests heavy-atom condensed-phase tunneling may be more important than currently assumed.
- Published
- 2021
27. Gaussian-Type Orbital Calculations for High Harmonic Generation in Vibrating Molecules: Benchmarks for H
- Author
-
Christoph, Witzorky, Guennaddi, Paramonov, Foudhil, Bouakline, Ralph, Jaquet, Peter, Saalfrank, and Tillmann, Klamroth
- Abstract
The response of the hydrogen molecular ion, H
- Published
- 2021
28. Condensed-phase isomerization through tunnelling gateways
- Author
-
Arnab Choudhury, Jessalyn A. DeVine, Shreya Sinha, Jascha A. Lau, Alexander Kandratsenka, Dirk Schwarzer, Peter Saalfrank, and Alec M. Wodtke
- Subjects
Multidisciplinary ,Isomerism ,Quantum Theory ,Thermodynamics - Abstract
Quantum mechanical tunnelling describes transmission of matter waves through a barrier with height larger than the energy of the wave1. Tunnelling becomes important when the de Broglie wavelength of the particle exceeds the barrier thickness; because wavelength increases with decreasing mass, lighter particles tunnel more efficiently than heavier ones. However, there exist examples in condensed-phase chemistry where increasing mass leads to increased tunnelling rates2. In contrast to the textbook approach, which considers transitions between continuum states, condensed-phase reactions involve transitions between bound states of reactants and products. Here this conceptual distinction is highlighted by experimental measurements of isotopologue-specific tunnelling rates for CO rotational isomerization at an NaCl surface3,4, showing nonmonotonic mass dependence. A quantum rate theory of isomerization is developed wherein transitions between sub-barrier reactant and product states occur through interaction with the environment. Tunnelling is fastest for specific pairs of states (gateways), the quantum mechanical details of which lead to enhanced cross-barrier coupling; the energies of these gateways arise nonsystematically, giving an erratic mass dependence. Gateways also accelerate ground-state isomerization, acting as leaky holes through the reaction barrier. This simple model provides a way to account for tunnelling in condensed-phase chemistry, and indicates that heavy-atom tunnelling may be more important than typically assumed.
- Published
- 2021
29. The electronic structure of the metal-organic interface of isolated ligand coated gold nanoparticles
- Author
-
Robin Schürmann, Evgenii Titov, Kenny Ebel, Sergio Kogikoski, Amr Mostafa, Peter Saalfrank, Aleksandar R. Milosavljević, and Ilko Bald
- Subjects
General Engineering ,General Materials Science ,Bioengineering ,General Chemistry ,Atomic and Molecular Physics, and Optics - Abstract
Light induced electron transfer reactions of molecules on the surface of noble metal nanoparticles (NPs) depend significantly on the electronic properties of the metal-organic interface. Hybridized metal-molecule states and dipoles at the interface alter the work function and facilitate or hinder electron transfer between the NPs and ligand. X-ray photoelectron spectroscopy (XPS) measurements of isolated AuNPs coated with thiolated ligands in a vacuum have been performed as a function of photon energy, and the depth dependent information of the metal-organic interface has been obtained. The role of surface dipoles in the XPS measurements of isolated ligand coated NPs is discussed and the binding energy of the Au 4f states is shifted by around 0.8 eV in the outer atomic layers of 4-nitrothiophenol coated AuNPs, facilitating electron transport towards the molecules. Moreover, the influence of the interface dipole depends significantly on the adsorbed ligand molecules. The present study paves the way towards the engineering of the electronic properties of the nanoparticle surface, which is of utmost importance for the application of plasmonic nanoparticles in the fields of heterogeneous catalysis and solar energy conversion.
- Published
- 2021
30. A thermofield-based multilayer multiconfigurational time-dependent Hartree approach to non-adiabatic quantum dynamics at finite temperature
- Author
-
Peter Saalfrank and Eric W. Fischer
- Subjects
Chemical Physics (physics.chem-ph) ,Physics ,Quantum dynamics ,Degrees of freedom (physics and chemistry) ,FOS: Physical sciences ,General Physics and Astronomy ,Hartree ,Physics - Chemical Physics ,Quantum mechanics ,ddc:540 ,Thermal ,Institut für Chemie ,ddc:530 ,Physical and Theoretical Chemistry ,Adiabatic process ,Representation (mathematics) ,Wave function ,Equivalence (measure theory) - Abstract
We introduce a thermofield-based formulation of the multilayer multiconfigurational time-dependent Hartree (ML-MCTDH) method to study finite temperature effects on non-adiabatic quantum dynamics from a non-stochastic, wave-function perspective. Our approach is based on the formal equivalence of bosonic many-body theory at zero temperature with doubled number of degrees of freedom and the thermal quasi-particle representation of bosonic thermofield dynamics (TFD). This equivalence allows for a transfer of bosonic many-body MCTDH as introduced by Wang and Thoss to the finite temperature framework of thermal quasi-particle TFD. As an application, we study temperature effects on the ultrafast internal conversion dynamics in pyrazine. We show, that finite temperature effects can be efficiently accounted for in the construction of multilayer expansions of thermofield states in the framework presented herein. Further, we find our results to agree well with existing studies on the pyrazine model based on the $\rho$MCTDH method., Comment: 34 pages, 7 figures; 24 Mode Pyrazine Linear Vibronic Coupling Model added
- Published
- 2021
31. Molecular Dynamics Simulation of the LOV2 Domain from Adiantum capillus-veneris.
- Author
-
Christian Neiss and Peter Saalfrank
- Published
- 2004
- Full Text
- View/download PDF
32. Quantum Chemistry Treatment of Silicon-Hydrogen Bond Rupture by Nonequilibrium Carriers in Semiconductor Devices
- Author
-
Foudhil Bouakline, Michael Waltl, Christoph Jungemann, Dominic Jabs, Al-Moatasem El-Sayed, Dominic Waldhör, Peter Saalfrank, M. Jech, Tibor Grasser, and Stanislav Tyaginov
- Subjects
010302 applied physics ,Materials science ,Silicon ,Condensed matter physics ,business.industry ,General Physics and Astronomy ,chemistry.chemical_element ,Non-equilibrium thermodynamics ,02 engineering and technology ,Semiconductor device ,021001 nanoscience & nanotechnology ,01 natural sciences ,Quantum chemistry ,chemistry ,0103 physical sciences ,MOSFET ,Microelectronics ,Charge carrier ,0210 nano-technology ,business ,Quantum - Abstract
Silicon-hydrogen bonds play a crucial role in modern microelectronics, especially regarding reliability. At the semiconductor-oxide interface these bonds are broken via interaction with energetic charge carriers, which spoils a MOSFET's performance, for example. This study develops a consistent physical picture of that phenomenon through a bottom-up approach based on quantum mechanical formulations, and also unravels the disparity of that effect in $n\ensuremath{-}$ and $p\ensuremath{-}$MOSFETs. The model is free of empirical parameters and can easily be extended to emerging material combinations.
- Published
- 2021
33. Many-electron dynamics in laser-driven molecules: wavefunction theory
- Author
-
Florian, Bedurke, Tillmann, Klamroth, and Peter, Saalfrank
- Abstract
With recent experimental advances in laser-driven electron dynamics in polyatomic molecules, the need arises for their reliable theoretical modelling. Among efficient, yet fairly accurate methods for many-electron dynamics are Time-Dependent Configuration Interaction Singles (TD-CIS) (a Wave Function Theory (WFT) method), and Real-Time Time-Dependent Density Functional Theory (RT-TD-DFT), respectively. Here we compare TD-CIS combined with extended Atomic Orbital (AO) bases, TD-CIS/AO, with RT-TD-DFT in a grid representation of the Kohn-Sham orbitals, RT-TD-DFT/Grid. Possible ionization losses are treated by complex absorbing potentials in energy space (for TD-CIS/AO) or real space (for RT-TD-DFT), respectively. The comparison is made for two test cases: (i) state-to-state transitions using resonant lasers (π-pulses), i.e., bound electron motion, and (ii) large-amplitude electron motion leading to High Harmonic Generation (HHG). Test systems are a H2 molecule and cis- and trans-1,2-dichlorethene, C2H2Cl2, (DCE). From time-dependent electronic energies, dipole moments and from HHG spectra, the following observations are made: first, for bound state-to-state transitions enforced by π-pulses, TD-CIS nicely accounts for the expected population inversion in contrast to RT-TD-DFT, in agreement with earlier findings. Secondly, when using laser pulses under non-resonant conditions, dipole moments and lower harmonics in HHG spectra are obtained by TD-CIS/AO which are in good agreement with those obtained with RT-TD-DFT/Grid. Deviations become larger for higher harmonics and at low laser intensities, i.e., for low-intensity HHG signals. We also carefully test effects of basis sets for TD-CIS/AO and grid size for RT-TD-DFT/Grid, different exchange-correlation functionals in RT-TD-DFT, and absorbing boundaries. Finally, for the present examples, TD-CIS/AO is observed to be at least an order of magnitude more computationally efficient than RT-TD-DFT/Grid.
- Published
- 2021
34. Non-Markovian vibrational relaxation dynamics at surfaces
- Author
-
Eric W. Fischer, Michael Werther, Foudhil Bouakline, Frank Grossmann, and Peter Saalfrank
- Subjects
Chemical Physics (physics.chem-ph) ,Physics - Chemical Physics ,FOS: Physical sciences ,General Physics and Astronomy ,Physical and Theoretical Chemistry - Abstract
Vibrational dynamics of adsorbates near surfaces plays both an important role for applied surface science and as model lab for studying fundamental problems of open quantum systems. We employ a previously developed model for the relaxation of a D-Si-Si bending mode at a D:Si(100)-(2$\times$1) surface, induced by a "bath" of more than $2000$ phonon modes [U. Lorenz, P. Saalfrank, Chem. Phys. {\bf 482}, 69 (2017)], to extend previous work along various directions. First, we use a Hierarchical Effective Mode (HEM) model [E.W. Fischer, F. Bouakline, M. Werther, P. Saalfrank, J. Chem. Phys. {\bf 153}, 064704 (2020)] to study relaxation of higher excited vibrational states than hitherto done, by solving a high-dimensional system-bath time-dependent Schr\"odinger equation (TDSE). In the HEM approach, (many) real bath modes are replaced by (much less) effective bath modes. Accordingly, we are able to examine scaling laws for vibrational relaxation lifetimes for a realistic surface science problem. Second, we compare the performance of the multilayer multiconfigurational time-dependent Hartree (ML-MCTDH) approach with the recently developed coherent-state based multi-Davydov D2 {\it ansatz} [N. Zhou, Z. Huang, J. Zhu, V. Chernyak, Y. Zhao, {J. Chem. Phys.} {\bf 143}, 014113 (2015)]. Both approaches work well, with some computational advantages for the latter in the presented context. Third, we apply open-system density matrix theory in comparison with basically "exact" solutions of the multi-mode TDSEs. Specifically, we use an open-system Liouville-von Neumann (LvN) equation treating vibration-phonon coupling as Markovian dissipation in Lindblad form to quantify effects beyond the Born-Markov approximation., Comment: 16 pages, 8 figures, v2: minor changes in abstract, v3: small changes after peer-review
- Published
- 2022
35. Raman Enhancement of Nanoparticle Dimers Self-Assembled Using DNA Origami Nanotriangles
- Author
-
Peter Saalfrank, Robert Edler von Zander, Sergio Kogikoski, Ilko Bald, and Kosti Tapio
- Subjects
surface-enhanced Raman scattering ,Materials science ,Dimer ,Pharmaceutical Science ,Nanoparticle ,Metal Nanoparticles ,resonance Raman scattering ,02 engineering and technology ,010402 general chemistry ,Microscopy, Atomic Force ,Spectrum Analysis, Raman ,01 natural sciences ,Molecular physics ,Article ,Analytical Chemistry ,lcsh:QD241-441 ,chemistry.chemical_compound ,symbols.namesake ,Computational Chemistry ,nanoparticle dimers ,Microscopy, Electron, Transmission ,lcsh:Organic chemistry ,Drug Discovery ,DNA origami ,Molecule ,Nanotechnology ,Physical and Theoretical Chemistry ,Particle Size ,Plasmon ,Density Functional Theory ,Organic Chemistry ,Resonance ,DNA ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,chemistry ,Chemistry (miscellaneous) ,symbols ,Microscopy, Electron, Scanning ,Molecular Medicine ,Gold ,0210 nano-technology ,Raman spectroscopy ,Dimerization ,Raman scattering - Abstract
Surface-enhanced Raman scattering is a powerful approach to detect molecules at very low concentrations, even up to the single-molecule level. One important aspect of the materials used in such a technique is how much the signal is intensified, quantified by the enhancement factor (EF). Herein we obtained the EFs for gold nanoparticle dimers of 60 and 80 nm diameter, respectively, self-assembled using DNA origami nanotriangles. Cy5 and TAMRA were used as surface-enhanced Raman scattering (SERS) probes, which enable the observation of individual nanoparticles and dimers. EF distributions are determined at four distinct wavelengths based on the measurements of around 1000 individual dimer structures. The obtained results show that the EFs for the dimeric assemblies follow a log-normal distribution and are in the range of 106 at 633 nm and that the contribution of the molecular resonance effect to the EF is around 2, also showing that the plasmonic resonance is the main source of the observed signal. To support our studies, FDTD simulations of the nanoparticle’s electromagnetic field enhancement has been carried out, as well as calculations of the resonance Raman spectra of the dyes using DFT. We observe a very close agreement between the experimental EF distribution and the simulated values.
- Published
- 2021
- Full Text
- View/download PDF
36. The role of structural flexibility in plasmon-driven coupling reactions : kinetic limitations in the dimerization of nitro-benzenes
- Author
-
Joachim Koetz, Robin Schürmann, Alexandar R. Milosavljevic, Tina Gaebel, Sergio Kogikoski, Amr Mostafa, Peter Saalfrank, Ferenc Liebig, Evgenii Titov, Wouter Koopman, Clemens N. Z. Schmitt, Ilko Bald, Felix Stete, Radwan M. Sarhan, and Matias Bargheer
- Subjects
Materials science ,Mechanical Engineering ,plasmon driven dimerization ,bimolecular photoreactions ,dimerization ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,Rate-determining step ,01 natural sciences ,Coupling reaction ,0104 chemical sciences ,Chemical kinetics ,Electron transfer ,chemistry.chemical_compound ,chemistry ,Mechanics of Materials ,Yield (chemistry) ,Molecule ,Density functional theory ,Methylene ,0210 nano-technology - Abstract
The plasmon-driven dimerization of 4-nitrothiophenol (4NTP) to 4-4’-dimercaptoazobenzene (DMAB) has become a testbed for understanding bimolecular photoreactions enhanced by nanoscale metals, in particular, regarding the relevance of electron transfer and heat transfer from the metal to the molecule. By adding a methylene group between the thiol bond and the nitrophenyl, we add structural flexibility to the reactant molecule. Time-resolved surface-enhanced Raman-spectroscopy proves that this (4-nitrobenzyl)mercaptan (4NBM) molecule has a larger dimerization rate and dimerization yield than 4NTP and higher selectivity towards dimerization. X-ray photoelectron spectroscopy and density functional theory calculations show that the electron transfer would prefer activation of 4NTP over 4NBM. We conclude that the rate limiting step of this plasmonic reaction is the dimerization step, which is dramatically enhanced by the additional flexibility of the reactant. This study may serve as an example for using nanoscale metals to simultaneously provide charge carriers for bond activation and localized heat for driving bimolecular reaction steps. The molecular structure of reactants can be tuned to control the reaction kinetics.
- Published
- 2021
37. On the Borate-Catalyzed Electrochemical Reduction of Phosphine Oxide: A Computational Study
- Author
-
Peter Saalfrank and Robert Edler von Zander
- Subjects
Phosphine oxide ,chemistry.chemical_compound ,Chemistry ,Photocatalysis ,chemistry.chemical_element ,Lewis acids and bases ,Physical and Theoretical Chemistry ,Triphenylphosphine ,Boron ,Electrochemistry ,Combinatorial chemistry ,Triphenylphosphine oxide ,Catalysis - Abstract
Recently, Nocera and co-workers (J. Am. Chem. Soc.2018, 140, 13711) demonstrated that triaryl borate Lewis acids facilitate the direct electrochemical reduction of triphenylphosphine oxide (TPPO) to triphenylphosphine (TPP). In the present contribution, we report a quantum chemical study unravelling details of the reaction, which also supports the proposed ECrECi mechanism. Alternative electrochemical routes to TPPO reduction facilitated by other Lewis acids (CH3+), or by photocatalysis at semiconductor surfaces, are also briefly discussed.
- Published
- 2020
38. Molecular attochemistry: Correlated electron dynamics driven by light
- Author
-
Tillmann Klamroth, Florian Bedurke, Peter Saalfrank, Mathias Nest, Chiara Heide, Jean Christophe Tremblay, Pascal Krause, Stefan Klinkusch, Institut für Chemie [Potsdam], Universität Potsdam, Freie Universität Berlin, Laboratoire de Physique et Chimie Théoriques (LPCT), and Institut de Chimie du CNRS (INC)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Physics ,010304 chemical physics ,Attosecond ,Physics::Optics ,Electron ,Laser ,01 natural sciences ,law.invention ,[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,Photoexcitation ,[PHYS.QPHY]Physics [physics]/Quantum Physics [quant-ph] ,law ,Ionization ,0103 physical sciences ,Femtosecond ,Physics::Atomic and Molecular Clusters ,High harmonic generation ,Physics::Atomic Physics ,Physics::Chemical Physics ,Atomic physics ,010306 general physics ,Ultrashort pulse ,ComputingMilieux_MISCELLANEOUS - Abstract
Modern laser technology and ultrafast spectroscopies have pushed the timescales for detecting and manipulating dynamical processes in molecules from the picosecond over femtosecond domains, to the attosecond regime (1 as = 10−18 s). This way, real-time dynamics of electrons after their photoexcitation can be probed and manipulated. In particular, experiments are moving more and more from atomic and solid state systems to molecules, opening the fields of “molecular electron dynamics” and “attosecond chemistry.” Also on the theory side, powerful quantum dynamical tools have been developed to rationalize experiments on ultrafast electron dynamics in molecular species. In this contribution, we concentrate on theoretical aspects of ultrafast electron dynamics in molecules, mostly driven by lasers. The dynamics will be described with the help of wavefunction-based ab initio methods such as time-dependent configuration interaction (TD-CI) or the multiconfigurational time-dependent Hartree-Fock (MCTDHF) methods. Besides a survey of the methods and their extensions toward, e.g., treatment of ionization, laser pulse optimization, and open quantum systems, two specific examples of applications will be considered: The creation and/or dynamical fate of electronic wavepackets, and the nonlinear optical response to laser pulse excitation in molecules by high harmonic generation (HHG).
- Published
- 2020
39. Two-Dimensional Nonlinear Optical Switching Materials: Molecular Engineering toward High Nonlinear Optical Contrasts
- Author
-
Clemens Rietze, Peter Saalfrank, Christoph Barta, Manuel Utecht, Karola Rück-Braun, Petra Tegeder, and Marc Hänsel
- Subjects
Materials science ,business.industry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Molecular engineering ,Photochromism ,Nonlinear optical ,General Energy ,Monolayer ,Optoelectronics ,Physical and Theoretical Chemistry ,Photonics ,0210 nano-technology ,business - Abstract
Combining photochromism and nonlinear optical (NLO) properties of molecular switches-functionalized self-assembled monolayers (SAMs) represents a promising concept toward novel photonic and optoele...
- Published
- 2018
40. Water Molecular Beam Scattering at α-Al2O3(0001): An Ab Initio Molecular Dynamics Study
- Author
-
Sophia Heiden, R. Kramer Campen, Jonas Wirth, and Peter Saalfrank
- Subjects
Thermal equilibrium ,Materials science ,Scattering ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,Dissociation (chemistry) ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Ab initio molecular dynamics ,General Energy ,Adsorption ,0103 physical sciences ,Translational energy ,Molecule ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,010306 general physics ,0210 nano-technology ,Molecular beam - Abstract
Recent molecular beam experiments have shown that water may adsorb molecularly or dissociatively on an α-Al2O3(0001) surface, with enhanced dissociation probability compared to “pinhole dosing”, i.e., adsorption under thermal equilibrium conditions. However, precise information on the ongoing reactions and their relative probabilities is missing. In order to shed light on molecular beam scattering for this system, we perform ab initio molecular dynamics calculations to simulate water colliding with α-Al2O3(0001). We find that single water molecules hitting a cold, clean surface from the gas phase are either reflected, molecularly adsorbed, or dissociated (so-called 1–2 dissociation only). A certain minimum translational energy (above 0.1 eV) seems to be required to enforce dissociation, which may explain the higher dissociation probability in molecular beam experiments. When the surface is heated and/or when refined surface and beam models are applied (preadsorption with water or water fragments, clusteri...
- Published
- 2018
41. Water Dissociative Adsorption on α-Al2O3(112̅0) Is Controlled by Surface Site Undercoordination, Density, and Topology
- Author
-
Harald Kirsch, Jonas Wirth, Sophia Heiden, Yanhua Yue, Peter Saalfrank, and R. Kramer Campen
- Subjects
Surface (mathematics) ,Work (thermodynamics) ,Materials science ,Ultra-high vacuum ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Dissociative adsorption ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Crystal ,General Energy ,Chemical physics ,ddc:540 ,Institut für Chemie ,Physical and Theoretical Chemistry ,0210 nano-technology ,Topology (chemistry) - Abstract
α-Al2O3 surfaces are common in a wide variety of applications and useful models of more complicated, environmentally abundant, alumino-silicate surfaces. While decades of work have clarified that all properties of these surfaces depend sensitively on the crystal face and the presence of even small amounts of water, quantitative insight into this dependence has proven challenging. Overcoming this challenge requires systematic study of the mechanism by which water interacts with various α-Al2O3 surfaces. Such insight is most easily gained for the interaction of small amounts of water with surfaces in ultra high vacuum. In this study, we continue our combined theoretical and experimental approach to this problem, previously applied to water interaction with the α-Al2O3 (0001) and (11̅02) surfaces, now to water interaction with the third most stable surface, that is, the (112̅0). Because we characterize all three surfaces using similar tools, it is straightforward to conclude that the (112̅0) is most reactive with water. The most important factor explaining its increased reactivity is that the high density of undercoordinated surface Al atoms on the (112̅0) surface allows the bidentate adsorption of OH fragments originating from dissociatively adsorbed water, while only monodentate adsorption is possible on the (0001) and (11̅02) surfaces: the reactivity of α-Al2O3 surfaces with water depends strongly, and nonlinearly, on the density of undercoordinated surface Al atoms.
- Published
- 2018
42. Control of Oxidation and Spin State in a Single-Molecule Junction
- Author
-
Lukas Braun, Nino Hatter, Christian Lotze, Katharina J. Franke, Peter Saalfrank, Benjamin W. Heinrich, and Christopher Ehlert
- Subjects
Materials science ,Spin states ,Scanning tunneling spectroscopy ,FOS: Physical sciences ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Molecular physics ,law.invention ,law ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Molecule ,ddc:530 ,General Materials Science ,oxidation state ,Physics::Chemical Physics ,Wave function ,density functional theory ,Condensed Matter - Mesoscale and Nanoscale Physics ,spin state ,500 Naturwissenschaften und Mathematik::530 Physik::530 Physik ,General Engineering ,Institut für Physik und Astronomie ,021001 nanoscience & nanotechnology ,Magnetocrystalline anisotropy ,0104 chemical sciences ,Intramolecular force ,scanning tunneling microscopy ,scanning tunneling spectroscopy ,Density functional theory ,Scanning tunneling microscope ,0210 nano-technology ,porphyrin - Abstract
The oxidation and spin state of a metal-organic molecule determine its chemical reactivity and magnetic properties. Here, we demonstrate the reversible control of the oxidation and spin state in a single Fe-porphyrin molecule in the force field of the tip of a scanning tunneling microscope. Within the regimes of half-integer and integer spin state, we can further track the evolution of the magnetocrystalline anisotropy. Our experimental results are corroborated by density functional theory and wave function theory. This combined analysis allows us to draw a complete picture of the molecular states over a large range of intramolecular deformations., Comment: Manuscript + Supplementary Information
- Published
- 2018
43. Cover Feature: Photoisomerization of an Azobenzene‐Containing Surfactant Within a Micelle (ChemPhotoChem 10/2021)
- Author
-
Peter Saalfrank, Svetlana Santer, Anjali Sharma, Nino Lomadze, Marek Bekir, and Evgenii Titov
- Subjects
Materials science ,Photoisomerization ,Organic Chemistry ,Surface hopping ,Photochemistry ,Micelle ,Analytical Chemistry ,chemistry.chemical_compound ,Reaction rate constant ,Azobenzene ,chemistry ,Pulmonary surfactant ,Feature (computer vision) ,Cover (algebra) ,Physical and Theoretical Chemistry - Published
- 2021
44. Publisher’s Note: 'Seemingly asymmetric atom-localized electronic densities following laser-dissociation of homonuclear diatomics' [J. Chem. Phys. 154, 234305 (2021)]
- Author
-
Foudhil Bouakline and Peter Saalfrank
- Subjects
Physics ,law ,General Physics and Astronomy ,Atom (order theory) ,Physical and Theoretical Chemistry ,Atomic physics ,Laser ,Diatomic molecule ,Dissociation (chemistry) ,Homonuclear molecule ,law.invention - Published
- 2021
45. Seemingly asymmetric atom-localized electronic densities following laser-dissociation of homonuclear diatomics
- Author
-
Foudhil Bouakline and Peter Saalfrank
- Subjects
Physics ,010304 chemical physics ,media_common.quotation_subject ,General Physics and Astronomy ,010402 general chemistry ,01 natural sciences ,Diatomic molecule ,Molecular physics ,Asymmetry ,Homonuclear molecule ,Symmetry (physics) ,0104 chemical sciences ,0103 physical sciences ,Atom ,Symmetry breaking ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Electronic density ,Identical particles ,media_common - Abstract
Recent experiments on laser-dissociation of aligned homonuclear diatomic molecules show an asymmetric forward-backward (spatial) electron-localization along the laser polarization axis. Most theoretical models attribute this asymmetry to interference effects between gerade and ungerade vibronic states. Presumably due to alignment, these models neglect molecular rotations and hence infer an asymmetric (post-dissociation) charge distribution over the two identical nuclei. In this paper, we question the equivalence that is made between spatial electron-localization, observed in experiments, and atomic electron-localization, alluded by these theoretical models. We show that (seeming) agreement between these models and experiments is due to an unfortunate omission of nuclear permutation symmetry, i.e., quantum statistics. Enforcement of the latter requires mandatory inclusion of the molecular rotational degree of freedom, even for perfectly aligned molecules. Unlike previous interpretations, we ascribe spatial electron-localization to the laser creation of a rovibronic wavepacket that involves field-free molecular eigenstates with opposite space-inversion symmetry i.e., even and odd parity. Space-inversion symmetry breaking would then lead to an asymmetric distribution of the (space-fixed) electronic density over the forward and backward hemisphere. However, owing to the simultaneous coexistence of two indistinguishable molecular orientational isomers, our analytical and computational results show that the post-dissociation electronic density along a specified space-fixed axis is equally shared between the two identical nuclei-a result that is in perfect accordance with the principle of the indistinguishability of identical particles.
- Published
- 2021
46. A novel system-bath Hamiltonian for vibration-phonon coupling: Formulation, and application to the relaxation of Si–H and Si–D bending modes of H/D:Si(100)-(2 × 1)
- Author
-
Peter Saalfrank and U. Lorenz
- Subjects
010304 chemical physics ,Antisymmetric relation ,Chemistry ,Phonon ,Band gap ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,symbols.namesake ,Orthogonal coordinates ,Quantum mechanics ,Excited state ,0103 physical sciences ,Vibrational energy relaxation ,symbols ,Density functional theory ,Physical and Theoretical Chemistry ,0210 nano-technology ,Hamiltonian (quantum mechanics) - Abstract
We present a rigorous method to set up a system-bath Hamiltonian for the coupling of adsorbate vibrations (the system) to surface phonons (the bath). The Hamiltonian is straightforward to derive and exact up to second order in the environment coordinates, thus capable of treating one- and two-phonon contributions to vibration-phonon coupling. The construction of the Hamiltonian uses orthogonal coordinates for system and bath modes, is based on an embedded cluster approach, and generalizes previous Hamiltonians of a similar type, but avoids several (additional) approximations. While the parametrization of the full Hamiltonian is in principle feasible by a first principles quantum mechanical treatment, here we adopt in the spirit of a QM/MM model a combination of density functional theory (“QM”, for the system) and a semiempirical forcefield (“MM”, for the bath). We apply the Hamiltonian to a fully H-covered Si(100)-(2 × 1) surface, using Fermi’s Golden Rule to obtain vibrational relaxation rates of various H–Si bending modes of this system. As in earlier work it is found that the relaxation is dominated by two-phonon contributions because of an energy gap between the Si–H bending modes and the Si phonon bands. We obtain vibrational lifetimes (of the first excited state) on the order of 2 ps at T = 0 K. The lifetimes depend only little on the type of bending mode (symmetric vs. antisymmetric, parallel vs. perpendicular to the Si2H2 dimers). They decrease by a factor of about two when heating the surface to 300 K. We also study isotope effects by replacing adsorbed H atoms by deuterium, D. The Si–D bending modes are shifted into the Si phonon band of the solid, opening up one-phonon decay channels and reducing the lifetimes to few hundred fs.
- Published
- 2017
47. Vibrationally Broadened Optical Spectra of Selected Radicals and Cations Derived from Adamantane: A Time-Dependent Correlation Function Approach
- Author
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Peter Saalfrank and Tao Xiong
- Subjects
Work (thermodynamics) ,010304 chemical physics ,Adamantane ,Radical ,Physics::Optics ,Diamond ,engineering.material ,010402 general chemistry ,Diamondoid ,01 natural sciences ,Molecular physics ,Optical spectra ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Correlation function ,ddc:540 ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,engineering ,Institut für Chemie ,Physical and Theoretical Chemistry - Abstract
Diamondoids are hydrogen-saturated molecular motifs cut out of diamond, forming a class of materials with tunable optoelectronic properties. In this work, we extend previous work on neutral, closed-shell diamondoids by computing with hybrid density functional theory and time-dependent correlation functions vibrationally broadened absorption spectra of cations and radicals derived from the simplest diamondoid, adamantane, namely, the neutral 1- and 2-adamantyl radicals (C10H15), the 1- and 2-adamantyl cations (C10H15+), and the adamantane radical cation (C10H16+). For selected cases, we also report vibrationally broadened emission, photoelectron, and resonance Raman spectra. Furthermore, the effect of the damping factor on the vibrational fine-structure is studied. The following trends are found: (1) Low-energy absorptions of the adamantyl radicals and cations, and of the adamantane cation, are all strongly red-shifted with respect to adamantane; (2) also, emission spectra are strongly red-shifted, whereas photoelectron spectra are less affected for the cases studied; (3) vibrational fine-structures are reduced compared to those of adamantane; (4) the spectroscopic signals of 1- and 2-adamantyl species are significantly different from each other; and (5) reducing the damping factor has only a limited effect on the vibrational fine-structure in most cases. This suggests that removing hydrogen atoms and/or electrons from adamantane leads to new optoelectronic properties, which should be detectable by vibronic spectroscopy.
- Published
- 2019
48. Vibrational spectra of dissociatively adsorbed D
- Author
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Giacomo, Melani, Yuki, Nagata, R Kramer, Campen, and Peter, Saalfrank
- Abstract
Water can adsorb molecularly or dissociatively onto different sites of metal oxide surfaces. These adsorption sites can be disentangled using surface-sensitive vibrational spectroscopy. Here, we model Vibrational Sum Frequency (VSF) spectra for various forms of dissociated, deuterated water on a reconstructed, Al-terminated α-Al
- Published
- 2019
49. A quantum-mechanical tier model for phonon-driven vibrational relaxation dynamics of adsorbates at surfaces
- Author
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Foudhil Bouakline, Eric W. Fischer, and Peter Saalfrank
- Subjects
Physics ,010304 chemical physics ,Phonon ,General Physics and Astronomy ,Lanczos algorithm ,Basis function ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Schrödinger equation ,symbols.namesake ,Quantum mechanics ,0103 physical sciences ,ddc:540 ,symbols ,Vibrational energy relaxation ,Institut für Chemie ,Physical and Theoretical Chemistry ,Physics::Chemical Physics ,Wave function ,Hamiltonian (quantum mechanics) ,Scaling - Abstract
We present a quantum-mechanical tier model for vibrational relaxation of low-lying excited states of an adsorbate vibrational mode (system), coupled to surface phonons (bath), at zero temperature. The tier model, widely used in studies of intramolecular vibrational energy redistribution in polyatomics, is adapted here to adsorbate-surface systems with the help of an embedded cluster approach, using orthogonal coordinates for the system and bath modes, and a phononic expansion of their interaction. The key idea of the model is to organize the system-bath zeroth-order vibrational space into a hierarchical structure of vibrational tiers and keep therein only vibrational states that are sequentially generated from the system-bath initial vibrational state. Each tier is generated from the previous one by means of a successor operator, derived from the system-bath interaction Hamiltonian. This sequential procedure leads to a drastic reduction of the dimension of the system-bath vibrational space. We notably show that for harmonic vibrational motion of the system and linear system-bath couplings in the system coordinate, the dimension of the tier-model vibrational basis scales as similar to N-lxv. Here, N is the number of bath modes, l is the highest-order of the phononic expansion, and l is the size of the system vibrational basis. This polynomial scaling is computationally far superior to the exponential scaling of the original zeroth-order vibrational basis, similar to M-N, with M being the number of basis functions per bath mode. In addition, since each tier is coupled only to its adjacent neighbors, the matrix representation of the system-bath Hamiltonian in this new vibrational basis has a symmetric block-tridiagonal form, with each block being very sparse. This favors the combination of the tier-model with iterative Krylov techniques, such as the Lanczos algorithm, to solve the time-dependent Schrodinger equation for the full Hamiltonian. To illustrate the method, we study vibrational relaxation of a D-Si bending mode, coupled via two-and (mainly) one-phonon interactions to a fully D-covered Si(100)-(2 x 1) surface, using a recent first-principles system-bath Hamiltonian. The results of the tier model are compared with those obtained by the Lindblad formalism of the reduced density matrix. We find that the tier model provides much more information and insight into mechanisms of vibration-phonon couplings at surfaces, and gives more reliable estimates of the adsorbate vibrational lifetimes. Moreover, the tier model might also serve as a benchmark for other approximate quantum-dynamics methods, such as multiconfiguration wavefunction approaches. Published under license by AIP Publishing.
- Published
- 2019
50. Vibrational response and motion of carbon monoxide on Cu(100) driven by femtosecond laser pulses: Molecular dynamics with electronic friction
- Author
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Steven Lindner, Robert Scholz, Maite Alducin, J. I. Juaristi, Ivor Lončarić, Peter Saalfrank, Jean Christophe Tremblay, German Research Foundation, Ministerio de Economía y Competitividad (España), Eusko Jaurlaritza, European Commission, Institut für Chemie [Potsdam], Universität Potsdam, Institut Ruđer Bošković (IRB), Laboratoire de Physique et Chimie Théoriques (LPCT), Institut de Chimie du CNRS (INC)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Universidad del Pais Vasco / Euskal Herriko Unibertsitatea [Espagne] (UPV/EHU), Centro de Fisica de Materiales (CFM), Consejo Superior de Investigaciones Científicas [Madrid] (CSIC)-Universidad del Pais Vasco / Euskal Herriko Unibertsitatea [Espagne] (UPV/EHU), Donostia International Physics Center (DIPC), and University of the Basque Country/Euskal Herriko Unibertsitatea (UPV/EHU)
- Subjects
Surface diffusion ,Physics ,010304 chemical physics ,Phonon ,Time evolution ,7. Clean energy ,01 natural sciences ,Molecular physics ,molecular dynamics ,Langevin equation ,[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,Molecular dynamics ,[PHYS.QPHY]Physics [physics]/Quantum Physics [quant-ph] ,Molecular vibration ,0103 physical sciences ,Potential energy surface ,ddc:540 ,Institut für Chemie ,Density functional theory ,010306 general physics ,ComputingMilieux_MISCELLANEOUS - Abstract
Carbon monoxide on copper surfaces continues to be a fascinating, rich microlab for many questions evolving in surface science. Recently, hot-electron mediated, femtosecond-laser pulse induced dynamics of CO molecules on Cu(100) were the focus of experiments [Inoue, Phys. Rev. Lett. 117, 186101 (2016)10.1103/PhysRevLett.117.186101] and theory [Novko, Phys. Rev. Lett. 122, 016806 (2019)10.1103/PhysRevLett.122.016806], unraveling details of the vibrational nonequilibrium dynamics on ultrashort (subpicoseconds) timescales. In the present work, full-dimensional time-resolved hot-electron driven dynamics are studied by molecular dynamics with electronic friction (MDEF). Dissipation is included by a friction term in a Langevin equation which describes the coupling of molecular degrees of freedom to electron-hole pairs in the copper surface, calculated from gradient-corrected density functional theory (DFT) via a local density friction approximation (LDFA). Relaxation due to surface phonons is included by a generalized Langevin oscillator model. The hot-electron induced excitation is described via a time-dependent electronic temperature, the latter derived from an improved two-temperature model. Our parameter-free simulations on a precomputed potential energy surface allow for excellent statistics, and the observed trends are confirmed by on-the-fly ab initio molecular dynamics with electronic friction (AIMDEF) calculations. By computing time-resolved frequency maps for selected molecular vibrations, instantaneous frequencies, probability distributions, and correlation functions, we gain microscopic insight into hot-electron driven dynamics and we can relate the time evolution of vibrational internal CO stretch-mode frequencies to measured data, notably an observed redshift. Quantitatively, the latter is found to be larger in MDEF than in experiment and possible reasons are discussed for this observation. In our model, in addition we observe the excitation and time evolution of large-amplitude low-frequency modes, lateral CO surface diffusion, and molecular desorption. Effects of surface atom motion and of the laser fluence are also discussed., This work was supported by the Deutsche Forschungsgemeinschaft (DFG), through project Sa 547/8-3. J.I.J. and M.A. acknowledge the Spanish Ministerio de Economía y Competitividad [Grant No. FIS2016-76471-P (AEI/FEDER, UE)] and Gobierno Vasco UPV/EHU project IT1246-19. I.L. was supported by the European Union through the European Regional Development Fund—the Competitiveness and Cohesion Operational Programme (KK.01.1.1.06).
- Published
- 2019
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