Search

The absolute photodetachment cross-section characterizes the photostability of atomic and molecular anions against photodestruction by neutralization. The measurement of this quantity has been reported only for atomic and simple molecular ions. In 2006, Wester's group introduced a novel ion trap-based technique to measure the absolute photodetachment cross-sections [S. Trippel et al., Phys. Rev. Lett. 97, 193003 (2006)]. In this letter, we present a novel methodology to streamline this technique to reduce the measurement time by several orders of magnitude by combining a single experimental rate measurement with a simulated column density distribution of the trapped ions. We used this technique to report the first such measurement for a molecule of biological interest, deprotonated indole, at a laser wavelength of 405 nm. The proposed scheme is anticipated to have a significant and transformative impact on the development of a comprehensive database for photodetachment and photodissociation cross-sections of molecular ions., Comment: 5 pages, 3 figures

We report the measurement of radiative lifetimes of the $6^1\Sigma_g^+(v=9,J=31)$ state of gas-phase molecular sodium using a high-resolution double-resonance spectroscopy. Measurements were done using a time-correlated photon counting technique at various pressures and temperatures. Lifetimes were extracted from extrapolations to the zero buffer gas pressure, called Stern-Volmer plot, and the temperature-dependence of the radiative lifetimes were measured over a temperature range from 593 K to 653 K. Our result agrees well within the error limits with the theoretical calculations., Comment: 13 pages, 8 figures

High-energy nuclear collisions were recently employed as an "imaging-by-smashing" tool to reveal the global shapes of colliding nuclei. Here, I explain how nuclear shapes become encoded during quark-gluon plasma formation and evolution, and how they can be decoded from final-state particle distributions. I highlight the method's potential to advance our understanding of nuclear structure and quark-gluon plasma physics., Comment: 6 pages, 4 figures

Methods for creating endofullerenes have been steadily improving since their discovery, allowing for new types of endofullerenes to be created in larger numbers. When a molecule is trapped in a fullerene, the fullerene creates a harmonic trapping potential that leaves most of the fundamental properties of the internal molecule intact. The fullerene cage does create a preferred axis for the internal molecule, which we refer to as the encapsulation-induced alignment of the molecule. We explore the alignment of AlF and N2 inside of C60 by first computing the interaction between the internal molecule and the fullerene cage using ab initio electronic structure methods. Our results show that the internal molecules are found to be strongly aligned despite finding that all the calculated spectroscopic constants are relatively unaffected by the fullerene cage., Comment: 9 pages, 8 figures, 2 tables

We develop double microwave shielding, which has recently enabled evaporative cooling to the first Bose-Einstein condensate of polar molecules [Bigagli et al., Nature 631, 289 (2024)]. Two microwave fields of different frequency and polarization are employed to effectively shield polar molecules from inelastic collisions and three-body recombination. Here, we describe in detail the theory of double microwave shielding. We demonstrate that double microwave shielding effectively suppresses two- and three-body losses. Simultaneously, dipolar interactions and the scattering length can be flexibly tuned, enabling comprehensive control over interactions in ultracold gases of polar molecules. We show that this approach works for a wide range of molecules. This opens the door to studying many-body physics with strongly interacting dipolar quantum matter.

It is well-known that water in both liquid and vapor phases exhibits exceptionally weak absorption of light in the visible range. Recent experiments, however, have demonstrated that at the liquid-air interface, absorption in the visible range is drastically increased. This increased absorption results in a rate of evaporation that exceeds the theoretical thermal limit by between two and five times. Curiously, the evaporation rate peaks at green wavelengths of light, while no corresponding absorptance peak has been observed. Experiments suggest that photons can cleave off clusters of water molecules at the surface, but no clear theoretical model has yet been proposed to explain how this is possible. This paper aims to present such a model and explain this surprising and important phenomenon., Comment: 10 pages, 4 figures; SI: 5 pages

Organic diradicals are envisioned as elementary building blocks for designing a new generation of spintronic devices and have been used in constructing prototypical field effect transistors and non-linear optical devices. Open-shell systems, however, are also reactive, thus requiring design strategies to protect their radical character from the environment, especially when they are embedded into solid-state devices. Here, we report the persistence on a metallic surface of the diradical character of a diindeno[b,i]anthracene (DIAn) core protected by bulky end-groups. Our scanning tunneling spectroscopy measurements on single-molecules detected singlet-triplet excitations that were absent for DIAn species packed in assembled structures. Density functional theory simulations unravel that molecular geometry on the metal substrate can crucially modify the value of the single-triplet gap via the delocalization of the radical sites. The persistence of the diradical character over metallic substrates is a promising finding for integrating radical-based materials in functional devices.

The structure of cyclo[18]carbon (C$_{18}$), whether in its polyynic form with bond length alternation (BLA) or its cumulenic form without BLA, has long fascinated researchers, even prior to its successful synthesis. Recent studies suggest a polyynic ground state and a cumulenic transient state; however, the dynamics remain unclear and lack experimental validation. This study presents a first-principles theoretical investigation of the bond lengths ($R_1$ and $R_2$) dependent two-dimensional potential energy surfaces (PESs) of C$_{18}$, concentrating on the ground state and carbon 1s ionized and excited states. We examine the potential of X-ray spectra for determining bond lengths and monitoring transient structures, finding that both X-ray photoelectron (XPS) and absorption (XAS) spectra are sensitive to these variations. Utilizing a library of ground-state minimum structures optimized with 14 different functionals, we observe that core binding energies predicted with the $\omega$B97XD functional can vary by 0.9 eV (290.3--291.2 eV). Unlike the ground state PES, which predicts minima at alternating bond lengths, the C1s ionized state PES predicts minima with equivalent bond lengths. In the XAS spectra, peaks 1$\pi^*$ and 2$\pi^*$ show a redshift with increasing bond lengths along the line where $R_1 = R_2$. Additionally, increasing $R_2$ (with $R_1$ fixed) results in an initial redshift followed by a blueshift, minimizing at $R_1 = R_2$. Major peaks indicate that both 1$\pi^*$ and 2$\pi^*$ arise from two channels: C1s$\rightarrow\pi^*_{z}$ (out-of-plane) and C1s$\rightarrow\pi^*_{xy}$ (in-plane) transitions at coinciding energies., Comment: 3 figures

We show that C$_{60}$ fullerene molecules can serve as promising building blocks in the construction of versatile crystal structures with unique symmetries using first-principles calculations. These phases include quasi-2D layered structures and 3D van der Waals crystals where the molecules adopt varied orientations. The interplay of molecular arrangement and lattice symmetry results in a variety of tuneable crystal structures with distinct properties. Specifically, the electronic structures of these phases vary significantly, offering potential for fine-tuning the band gap for electronics and optoelectronics. Additionally, the optical properties of these materials are strongly influenced by their crystalline symmetry and molecular alignment, providing avenues for tailoring optical responses for photonics. Our findings highlight the potential of fullerene-based building blocks in the rational design of functional materials., Comment: 6 pages, 4 figures

High-resolution X-ray spectroscopy is an essential tool in X-ray astronomy, enabling detailed studies of celestial objects and their physical and chemical properties. However, comprehensive mapping of high-resolution X-ray spectra for even simple interstellar and circumstellar molecules is still lacking. In this study, we conducted systematic quantum chemical simulations to predict the C1s X-ray absorption spectra of CN$^+$, CN, and CN$^-$. Our findings provide valuable references for both X-ray astronomy and laboratory studies. We assigned the first electronic peak of CN$^+$ and CN to C1s $\rightarrow \sigma^*$ transitions, while the peak for CN$^-$ corresponds to a C1s $\rightarrow \pi^*$ transition. We further calculated the vibronic fine structures for these transitions using the quantum wavepacket method based on multiconfigurational-level, anharmonic potential energy curves, revealing distinct energy positions for the 0-0 absorptions at 280.7 eV, 279.6 eV, and 285.8 eV. Each vibronic profile features a prominent 0-0 peak, showing overall similarity but differing intensity ratios of the 0-0 and 0-1 peaks. Notably, introducing a C1s core hole leads to shortened C-N bond lengths and increased vibrational frequencies across all species. These findings enhance our understanding of the electronic structures and X-ray spectra of carbon-nitrogen species, emphasizing the influence of charge state on X-ray absorptions., Comment: 4 figures

The existence of macroscopic shell structure of submicron metal clusters is known for several decades. Since the most studies provide theoretical analysis for clusters of spherical shape, the electron density inhomogeneities caused by shell effects are spherically symmetric and do not provide long range electrostatic fields. However, similar shell structure should exist in a hemispherical cluster which conserves the closed periodic orbits of electrons, but not the spherical symmetry of electron distribution. As a result, we demonstrate that a strong electrostatic field ($E \sim 10^8$~V/m) exists in the vicinity of the flat surface of an isolated, uncharged metal nanocluster of hemispherical shape using modern approaches for electronic structure evaluation. This physical phenomenon is a consequence of the large-scale spatial inhomogeneity in distribution of electrons related to quantum shell effects in submicron metal clusters, which may find numerous applications in various fields of science and technology., Comment: 6 pages, 3 figures; typos corrected

Spherical Harmonic Gaussian type orbitals and Slater functions can be expressed using spherical coordinates or a linear combinations of the appropriate Cartesian functions. General expressions for the transformation coefficients between the two representations are provided. Values for the transformation coefficients are tabulated up to the quantum number $\ell = 10$.

The origin of the magnetic quadrupole (MQ) interactions in Gd$_{3}$Ru$_{4}$Al$_{12}$ which is known as a frustrated spin system and as a host material of skyrmion with a sentrosymmetric crystal structure are discussed. The MQ interactions between ferromagnetic (FM) spin trimers with imperfect FM directivity are deduced from synthesis of dipole Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. The Hamiltonian which includes both the MQ interactions and dipole interactions is proposed, and magnetic anisotropies, magnetic phase transitions and contribution of the MQ interactions to stabilize the skyrmion lattice (SkL) are discussed based on this Hamiltonian. Degrees of MQ freedom carried by the trimers contribute to stabilizing SkL which appears at finite temperatures., Comment: 25 pages, 28 figures

X-ray free-electron lasers (XFELs) are renowned for their high brightness, significantly impacting biology, chemistry, and nonlinear X-ray optics. However, current XFELs are large, expensive, and exhibit significant shot-to-shot instability. Here, we propose a novel compact apparatus for generating X-ray lasers. The setup integrates an ion source to produce highly charged ions as the gain medium. The X-ray optical cavity employs crystal Bragg diffraction for high reflectivity at large angles, and two parabolic compound refractive lenses (CRLs) focus the X-rays. Pumping is achieved through electron collision excitations. This X-ray laser offers compact dimensions, reduced costs, and enhanced coherence, positioning it as a promising seed for XFELs. With further optimization, this device has the potential to rival XFELs and revolutionize both scientific research and industrial applications., Comment: 7 pages, 1 figure

High spin-Chern-number topological phases provide a promising low-dimensional platform for realizing double-helical edge states. In this letter, we show how these edge states can host a variety of phases driven by electron interaction effects, including multi-channel helical Luttinger liquid, spin density wave, superconducting phases, and a new type of $\pi$-junction analog of the latter two, where the transitions between the phases can be controlled. The superconducting phase in the interacting system is shown to be adiabatically connected to a time-reversal-symmetric topological superconductor in the non-interacting DIII class. This connection stabilizes Majorana Kramers pairs as domain wall states at the interface between the superconducting and $\pi$-spin-density wave phases, with the latter exhibiting a time-reversal-symmetric spin-density wave phase. We discuss the possibility of realizing our proposed scheme for generating Majorana Kramers pairs in a cold-atom based platform with existing techniques, and how it could offer potential advantages over other approaches., Comment: 23 pages, 7 figures

Upon absorbing a photon, the ionized electron sails through the target force field in attoseconds to reach free space. This navigation probes details of the potential landscape that get imprinted into the phase of the ionization amplitude. The Eisenbud-Wigner-Smith (EWS) time delay, the energy derivative of this phase, provides the navigation time relative to the time of the electron's ``free'' exit. This time is influenced by the diffraction of the electron from the potential landscape, offering structural and dynamical information about interactions. If the potential has an intrinsic symmetry, a regular pattern in the time delay, including subpatterns of delays and advances, may occur from the diffraction process. The recent synthesis of a polyhedral fluorocarbon instigates the current study of photoionization from a cubic molecule. Our simulation of the EWS delay unravels rich diffraction motifs within $\pm$100 attoseconds in both energy and angular distributions. Averaging over the Euler angles from the laboratory to the molecular frame and over the photoelectron azimuthal direction indicates that the pattern should be discernible in ultrafast chronoscopy. The study benchmarks diffraction in molecular photoionization as a fundamental process which can be experimentally accessed through ultrafast time delay.

We investigate a shift in the critical temperature of rotating Bose-Einstein condensates mediated by the melting of the vortex lattice. Numerical simulations reveal that this temperature exhibits contrasting behavior depending on the system configuration: a negative shift occurs for fixed trap potentials due to the expansion of the condensate, while a positive shift is observed for fixed volumes, where vortex lattice rigidity suppresses thermal fluctuations. We introduce a vortex-energy model that captures the role of vortex interactions, the positional energy of the vortex lattice, as well as the phase transition and how the vortex lattice disappears. The findings provide insights into the thermodynamic properties of rotating condensates and the dynamics of vortex lattice melting, offering potential parallels with other quantum systems such as type-II superconductors.

Irradiation of condensed matter with ionizing radiation generally causes direct photoionization as well as secondary processes that often dominate the ionization dynamics. Here, large helium (He) nanodroplets with radius >40 nm doped with lithium (Li) atoms are irradiated with extreme ultraviolet (XUV) photons of energy >44.4 eV and indirect ionization of the Li dopants is observed in addition to direct photoionization of the He droplets. Specifically, Li ions are efficiently produced by an interatomic Coulombic decay (ICD) process involving metastable He atoms and He_2 excimers which are populated by elastic and inelastic scattering of photoelectrons in the nanodroplets as well as by electron-ion recombination. This type of indirect ICD, observed in large He nanodroplets in nearly the entire XUV range, turns out to be more efficient than Li dopant ionization by ICD following direct resonant photoexcitation at a photon energy of 21.6 eV and by charge-transfer ionization. Indirect ICD processes induced by scattering of photoelectrons likely play an important role in other condensed phase systems exposed to ionizing radiation as well, including biological matter.

Computing high dimensional potential surfaces for molecular and materials systems is considered to be a great challenge in computational chemistry with potential impact in a range of areas including fundamental prediction of reaction rates. In this paper we design and discuss an algorithm that has similarities to large language models in generative AI and natural language processing. Specifically, we represent a molecular system as a graph which contains a set of nodes, edges, faces etc. Interactions between these sets, which represent molecular subsystems in our case, are used to construct the potential energy surface for a reasonably sized chemical system with 51 dimensions. Essentially a family of neural networks that pertain to the graph-based subsystems, get the job done for this 51 dimensional system. We then ask if this same family of lower-dimensional neural networks can be transformed to provide accurate predictions for a 186 dimensional potential surface. We find that our algorithm does provide reasonably accurate results for this larger dimensional problem with sub-kcal/mol accuracy for the higher dimensional potential surface problem.

We show that a nonchiral atom can act as an antenna to induce a photoelectron circular dichroism in a nearby chiral molecule in a three-step process: The donor atom (antenna) is initially resonantly excited by circularly polarized radiation. It then transfers its excess energy to the acceptor molecule by means of resonant interatomic Coulombic decay. The latter finally absorbs the energy and emits an electron which exhibits the aforementioned circular dichroism in its angular distribution. We study the process on the basis of the retarded dipole--dipole interaction and report an asymptotic analytic expression for the distance-dependent chiral asymmetry of the photoelectron as induced by resonant interatomic Coulombic decay for random line-of-sight and acceptor orientations. In the nonretarded limit, the predicted chiral asymmetry is reversed as compared to that of a direct photoelectron circular dichroism of the molecule.

While photodissociation of molecular systems has been extensively studied, the photoinduced formation of chemical bonds remains largely unexplored. Especially for larger aggregates, the electronic and nuclear dynamics involved in the cluster formation process remain elusive. This limitation is rooted in difficulties to prepare reactants at well-defined initial conditions. Here, we overcome this hurdle by exploiting the exceptional solvation properties of helium nanodroplets. We load the droplets with Mg atoms and investigate the dynamical response of the formed Mg$_n$ aggregates to photoexcitation with time-resolved photoelectron spectroscopy. Beside the response expected for conventional Mg$_n$ clusters, consisting of a prompt signal rise and a decay characteristic for van der Waals bonds, the transient spectra also show a delayed photoelectron band peaking at 1.2 ps. This delayed signal rise is characteristic for nuclear dynamics and represents the transition of Mg$_n$ aggregates from a metastable, foam-like configuration, where Mg atoms are stabilized with a previously predicted interatomic spacing of 9.5 A, to a compact cluster. With global fitting analysis and ion-electron coincidence detection, the concerted electronic and nuclear dynamics can be tracked on a fs timescale. We find that cluster formation, proceeding with a ($450\pm180$) fs time constant, is accompanied by the population of highly-excited atomic states. We propose an energy pooling reaction in collisions of two or more excited Mg atoms during cluster formation as the mechanism leading to population of these high-lying Mg states. Additionally, conversion to kinetic energy through electronic relaxation leads to fragmentation and ejection of ionic cluster fragments from the He droplet. These results underline the potential of He droplets for time-resolved studies of bond formation and to uncover involved processes.

Most widely used machine learned (ML) potentials for condensed phase applications rely on many-body permutationally invariant polynomial (PIP) or atom-centered neural networks (NN). However, these approaches often lack chemical interpretability in atomistic energy decomposition and the computational efficiency of traditional force fields has not been fully achieved. Here, we present a novel method that combines aspects of both approaches, and achieves state-of-the-art balance of accuracy and force field-level speed. This method utilizes a monomer-centered representation, where the potential energy is decomposed into the sum of chemically meaningful monomeric energies. Without sophisticated neural network design, the structural descriptors of monomers are described by 1-body and 2-body effective interactions, enforced by appropriate sets of PIPs as inputs to the feed forward NN. We demonstrate the performance of this method through systematic assessments of models for gas-phase water trimer, liquid water, and also liquid CO2. The high accuracy, fast speed, and flexibility of this method provide a new route for constructing accurate ML potentials and enabling large-scale quantum and classical simulations for complex molecular systems.

Recent experiments have demonstrated that vibrational strong coupling (VSC) between molecular vibrations and the optical cavity field can modify vibrational energy transfer (VET) processes in molecular systems. However, the underlying mechanisms and the behavior of individual molecules under collective VSC remain largely incomplete. In this work, we combine state-of-the-art quantum vibrational spectral calculation, quantum wavepacket dynamics simulations, and ab initio machine-learning potential to elucidate how the vibrational dynamics of water OH stretches can be altered by VSC. Taking the (H$_2$O)$_{21}$-cavity system as an example, we show that the collective VSC breaks the localization picture, promotes the delocalization of OH stretches, and opens new intermolecular vibrational energy pathways involving both neighboring and remote water molecules. The manipulation of the VET process relies on the alignment of the transition dipole moment orientations of the corresponding vibrational states. The emergence of new energy transfer pathways is found to be attributed to cavity-induced vibrational resonance involving OH stretches across different water molecules, along with alterations in mode coupling patterns. Our fully quantum theoretical calculations not only confirm and extend previous findings on cavity-modified energy transfer processes but also provide new insights in energy transfer processes under collective VSC.

Vibrational wave packets are created in the lowest triplet state \triplet of $\mathrm{K_2}$ and $\mathrm{Rb_2}$ residing on the surface of helium nanodroplets, through non-resonant stimulated impulsive Raman scattering induced by a moderately intense near-infrared laser pulse. A delayed, intense 50-fs laser pulse doubly ionizes the alkali dimers via multiphoton absorption and thereby causes them to Coulomb explode into a pair of alkali ions $\mathrm{Ak^+}$. From the kinetic energy distribution $P(E_\mathrm{kin})$ of the $\mathrm{Ak^+}$ fragment ions, measured at a large number of delays, we determine the time-dependent internuclear distribution $P(R,t)$, which represents the modulus square of the wave packet within the accuracy of the experiment. For both $\mathrm{K_2}$ and $\mathrm{Rb_2}$, $P(R,t)$ exhibits a periodic oscillatory structure throughout the respective 300 ps and 100 ps observation times. The oscillatory structure is reflected in the time-dependent mean value of $R$, $\langle R \rangle(t)$. Fourier transformation of $\langle R \rangle(t)$ shows that the wave packets are composed mainly of the vibrational ground state and the first excited vibrational state, in agreement with numerical simulations. In the case of $\mathrm{K_2}$, the oscillations are observed for 300 ps corresponding to more than 180 vibrational periods with an amplitude that decreases gradually from 0.035 {\AA} to 0.020 {\AA}. Using time-resolved spectral analysis, we find that the decay time of the amplitude is $\sim$ 260 ps. The decrease is ascribed to the weak coupling between the vibrating dimers and the droplet.

We present a high-precision solution of Dirac equation by numerically solving the minmax two-center Dirac equation with the finite element method (FEM). The minmax FEM provide a highly accurate benchmark result for systems with light or heavy atomic nuclear charge $Z$. A result is shown for the molecular ion ${\rm H}_2^+$ and the heavy quasi-molecular ion ${\rm Th}_2^{179+}$, with estimated fractional uncertainties of $\sim 10^{-23}$ and $\sim 10^{-21}$, respectively. The result of the minmax-FEM high-precision of the solution of the two-center Dirac equation, allows solid control over the required accuracy level and is promising for the application and extension of our method.

The formation of Li$_2^+$ and subsequently Li$^+$ ions, during the excitation of $^7$Li atoms to the $3S_{1/2}$ state in a $^7$Li magneto optical trap (MOT), is probed in an ion-atom hybrid trap. Associative ionization occurs during the collision of Li($2P_{3/2}$) and Li($3S_{1/2}$) ultracold atoms, creating Li$_2^+$ ions. Photodissociation of Li$_2^+$ by the MOT lasers is an active channel for the conversion of Li$_2^+$ to Li$^+$. A fraction of the Li$_2^+$ ions is long lived even in the presence of MOT light. Additionally, rapid formation of Li$^+$ from Li$_2^+$ in the absence of MOT light is observed. Resonant excitation of ultracold atoms, resulting in intricate molecular dynamics, reveals important processes in ultracold dilute gases., Comment: The submitted manuscript consists of 10 pages including references. It consists of 11 figures including the figures in the supplemental material

In the present work, the low-lying structures of 20 different-sized water clusters are extensively searched using the artificial bee colony algorithm with TIP4P classical force field. To obtain the lowest equilibrium geometries, we select the 10 lowest configurations for further minimization using density functional theory. The resulting structures are lower in energy than previously reported results. The structural and energetic stability of these clusters are studied using various descriptors such as binding energy, ionization potentials, fragmentation energy, first and second energy difference, vibrational and optical spectra. The energetic analysis shows that clusters with N = 4, 8, 12, 14, 16 and 19 are more stable. The analysis of fragmentation energies also supports these findings. Our calculations show that non-covalent interactions play a significant role in stabilizing the water clusters. The infrared spectra of water clusters display three distinct bands: intermolecular O...H vibrations, 23 to 1191 cm^-1, intramolecular H-O-H bending, 1600 to 1741 cm^-1, and O-H stretching, 3229 to 3877 cm^-1. The strongest intensity is observed in the low-frequency symmetric stretching modes, along with a noticeable red shift in the stretching vibrations. The optical band gap ranges from 7.14 eV to 8.17 eV and lies in the ultraviolet region. The absorption spectra also show line broadening for clusters with n>=10, resulting in an increase in spectral lines. Interestingly, only the stable clusters exhibit maximum oscillator strength, with the first excitation in all cases corresponding to a \pi-to-\sigma* transition., Comment: 17 pages, 18 figures

Typical path integral Monte Carlo approaches use the primitive approximation to compute the probability density for a given path. In this work, we develop the pair Discrete Variable Representation (pair-DVR) approach to study molecular rotations. The pair propagator, which was initially introduced to study superfluidity in condensed Helium, is naturally well-suited for systems interacting with a pair-wise potential. Consequently, paths sampled using the pair action tend to be closer to the exact paths (compared to primitive Trotter paths) for such systems leading to convergence with less imaginary time steps. Therefore, our approach relies on using the pair factorization approach in conjunction with a discretized Path Integral Ground State (PIGS) paradigm to study a chain of planar rotors interacting with a pair-wise dipole interaction. We first use the Wigner-Kirkwood density expansion to analyze the asymptotics of the pair propagator in imaginary time. Then, we exhibit the utility of the pair factorization scheme via convergence studies comparing the pair and primitive propagators. Finally, we compute energetic and structural properties of this system including the correlation function and Binder ratio as functions of the coupling strength to examine the behaviour of the pair-DVR method near criticality. Density Matrix Renormalization Group results are used for benchmarking throughout.

Benefiting from improved stability due to stronger interlayer van der Waals interactions, few-layer fullerene networks are experimentally more accessible compared to monolayer polymeric C$_{60}$. However, there is a lack of systematic theoretical studies on the material properties of few-layer C$_{60}$ networks. Here, we compare the structural, electronic and optical properties of bilayer and monolayer fullerene networks. The band gap and band-edge positions remain mostly unchanged after stacking two layers into a bilayer, enabling the bilayer to be almost as efficient a photocatalyst as the monolayer. The effective mass ratio along different directions is varied for conduction band states due to interlayer interactions,leading to enhanced anisotropy in carrier transport. Additionally, stronger exciton absorption is found in the bilayer than that in the monolayer over the entire visible light range, rendering the bilayer a more promising candidate for photovoltaics. Moreoever, the polarisation dependence of optical absorption in the bilayer is increased in the red-yellow light range, offering unique opportunities in photonics and display technologies with tailored optical properties over specific directions. Our study provides strategies to tune electronic and optical properties of 2D polymeric C$_{60}$ via the introduction of stacking degrees of freedom., Comment: 7 pages, 4 figures

In this work, we propose a decoupled support vector regression (SVR) approach for direct canonical polyadic decomposition (CPD) of a potential energy surface (PES) through a set of discrete training energy data. This approach, denoted by CPD-SVR, is able to directly construct the PES in CPD with a more compressed form than previously developed Gaussian process regression (GPR) for CPD, denoted by CPD-GRP ({\it J. Phys. Chem. Lett.} {\bf 13} (2022), 11128). Similar to CPD-GPR, the present CPD-SVR method requires the multi-dimension kernel function in a product of a series of one-dimensional functions. We shall show that, only a small set of support vectors play a role in SVR prediction making CPD-SVR predict lower-rank CPD than CPD-GPR. To save computational cost in determining support vectors, we propose a warm-started (ws) algorithm where a pre-existed crude PES is employed to classify the training data. With the warm-started algorithm, the present CPD-SVR approach is extended to the CPD-ws-SVR approach. Then, we test CPD-ws-SVR and compare it with CPD-GPR through constructions and applications of the PESs of H + H$_2$, H$_2$ + H$_2$, and H$_2$/Cu(111). To this end, the training data are computed by existed PESs. Calculations on H + H$_2$ predict a good agreement of dynamics results among various CPD forms, which are constructed through different approaches.

In high-resolution mass spectrometry, an electrospray ionization source is often paired with an ion-funnel to enhance ion transmission. Although it is established that ions experience collision-induced dissociation as they pass through this device, the impact of gas-flow dynamics on ion fragmentation remains unexplored. The present work demonstrates that the gas-flow dynamics from the capillary interface of an electrospray ionization source into an ion-funnel significantly reduces ion fragmentation. This reduction stems from the substantial decrease in the rate of increase in the internal energy of the ions resulting from the collisions with a supersonically expanding gas. The results of this study have significant consequences for systems that employ electrospray mass spectrometry and ion-mobility spectrometry.

Training interatomic potentials for spin-polarized systems continues to be a difficult task for the molecular modeling community. In this note, a proof-of-concept, random initial spin committee approach is proposed for obtaining the ground state of spin-polarized systems with a controllable degree of accuracy. The approach is tested on two toy models of elemental sulfur where the exact optimal spin configuration can be known. Machine-learning potentials are trained on the resulting data, and increasingly accurate fits with respect to the ground state are achieved, marking a step towards machine-learning force fields for general bulk spin-polarized systems., Comment: The supporting data will be uploaded at https://doi.org/10.17863/CAM.112212 after the publication is accepted

Elucidating the significance of low-energy electrons in the rupture of DNA/RNA and the process involved in it is crucial in the field of radiation therapy. Capturing of the incident electron in one of the empty molecular orbitals and the formation of a temporary negative ion (TNI) is considered to be a stepping stone towards the lesion of DNA/RNA. This TNI formation manifests itself as a resonance peak in the cross-sections determined for the electron-molecule interaction. In the present work, we have reported the integral (ICS), differential (DCS), and momentum transfer (MTCS) cross-sections for the elastic scattering of low-energy electrons from the isomers, 2H-pyran and 4H-pyran $\rm{(C_5H_6O)}$, which are analogues of the sugar backbone of DNA. The single-center expansion method has been employed for the scattering calculations. Further, we have used the time delay approach to identify and analyze the resonance peaks. Our results for the ICS and DCS compare well with the only data available in the literature. MTCS data for 2H-pyran and 4H-pyran have been reported for the first time. Moreover, we have also identified an extra peak for each molecule, from time delay analysis, which might be a potential resonance.

In this work, we propose a Path Integral Monte Carlo (PIMC) approach based on discretized continuous degrees of freedom and rejection-free Gibbs sampling. The ground state properties of a chain of planar rotors with dipole-dipole interactions are used to illustrate the approach. Energetic and structural properties are computed and compared to exact diagonalization and Numerical Matrix Multiplication for $N \leq 3$ to assess the systematic Trotter factorization error convergence. For larger chains with up to N = 100 rotors, Density Matrix Renormalization Group (DMRG) calculations are used as a benchmark. We show that using Gibbs sampling is advantageous compared to traditional Metroplolis-Hastings rejection importance sampling. Indeed, Gibbs sampling leads to lower variance and correlation in the computed observables.

The COVID-19 pandemic has profoundly impacted global economies and healthcare systems, revealing critical vulnerabilities in both. In response, our study introduces a groundbreaking method for the detection of SARS-CoV-2 cDNA, leveraging Luminescence resonance energy transfer (LRET) between upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs) to achieve an unprecedented detection limit of 242 femtomolar (fM). This innovative sensing platform utilizes UCNPs conjugated with one primer and AuNPs with another, targeting the 5' and 3' ends of the SARS-CoV-2 cDNA, respectively, enabling precise differentiation of mismatched DNA sequences and significantly enhancing detection specificity. Through rigorous experimental analysis, we established a quenching efficiency range from 10.4\% to 73.6\%, with an optimal midpoint of 42\%, thereby demonstrating the superior sensitivity of our method. By comparing the quenching efficiency of mismatched DNAs to the target DNA, we identified an optimal DNA:UCNP:AuNP ratio that ensures accurate detection. Our comparative analysis with existing SARS-CoV-2 detection methods revealed that our approach not only provides a lower detection limit but also offers higher specificity and potential for rapid, on-site testing. This study demonstrates the superior sensitivity and specificity of using UCNPs and AuNPs for SARS-CoV-2 cDNA detection, offering a significant advancement in rapid, accessible diagnostic technologies. Our method, characterized by its low detection limit and high precision, represents a critical step forward in managing current and future viral outbreaks, contributing to the enhancement of global healthcare responsiveness and infectious disease control., Comment: 14 pages, 5 figs

Ruling a wide range of phenomena, dipole-dipole interactions (DDI) are typically constrained to the short range due to their rapid decay with the increasing dipole separations, limiting the performance in long-range applications. By judiciously designing the photonic structures that control the two-point Green's functions of the electromagnetic environment, the spontaneous emission of quantum emitters (luminescence) and their interactions (e.g., F\"orster energy transfer) can be conveniently tuned. In this paper, we designed a matched nanoparticle-on-mirror antenna pair with enhanced DDI guided by surface plasmon polaritons confined to the metal substrate, which ensures concentrated and enhanced interaction over long ranges of tens of wavelengths. The long-range ($\sim 10 \lambda$) DDI between donor-acceptor emitters is enhanced by $6\times 10^{3}$ times respective to bare gold film, and $4.4\times 10^{4}$ times respective to vacuum. Our result provides a promising testbed for investigating long-range DDI phenomena on the nanoscale.

The 'l-Doubling' phenomenon emanates from the coupling between molecular rotations and perpendicular vibrations (bending modes) in polyatomic molecules. This elusive phenomenon has been largely discarded in laser-induced molecular alignment. Here we explore and unveil the ramifications of 'l-Doubling' to the coherent rotational dynamics of triatomic molecules at ambient temperatures and above. The observed 'l-Doubling' dynamics may be wrongly considered as collisional decay throughout the first few hundreds of picoseconds past excitation, highlighting the importance of correct assimilation of l-Doubling in current research of dissipative rotational dynamics and in coherent rotational dynamics in general., Comment: 9 pages, including supplementary information

The catalytic activities of high-spin small Fe(III) oxides have been investigated for efficient hydrogen production through ammonia decomposition, using the Artificial Force Induced Reaction (AFIR) method within the framework of density functional theory (DFT) with the B3LYP hybrid exchange-correlation functional. Our results reveal that the adsorption free energy of NH$_3$ on (Fe$_2$O$_3$)$_n$ ($n=1-4$) decreases with increasing cluster size up to $n=3$, followed by a slight increase at $n=4$. The strongest NH$_3$ adsorption energy, 33.68 kcal/mol, was found for Fe$_2$O$_3$, where NH$_3$ interacts with a two-coordinated Fe site, forming an Fe-N bond with a length of 2.11 \AA. A comparative analysis of NH$_3$ decomposition and H$_2$ formation on various Fe(III) oxide sizes identifies the rate-determining steps for each reaction. We found that the rate-determining step for the full NH$_3$ decomposition on (Fe$_2$O$_3$)$_n$ ($n=1-4$) is size-dependent, with the NH$^{*}$ $\rightleftharpoons$ N$^{*}$ + 3H$^{*}$ reaction acting as the limiting step for $n=1-3$. Additionally, our findings indicate that H$_2$ formation is favored following the partial decomposition of NH$_3$ on Fe(III) oxides.

The Chern number is a crucial topological invariant for distinguishing the phases of Chern insulators. Here we find that for Chern insulators with inversion symmetry, the Chern number alone is insufficient to fully characterize their topology. Specifically, distinct topological phases can be differentiated based on skyrmions at different high-symmetry points. Interfaces between these topological phases exhibit gapless helical states, which provide counter-propagating transport channels and robust quantized transport. Additionally, we identify topological transitions that do not involve changes in the Chern number but can be characterized by transitions of skyrmions between high-symmetry points. These transitions arise due to the toroidal structure of the two-dimensional Brillouin zone, which is generally applicable to two-dimensional periodic lattice system. Our research introduces new degrees of freedom for controlling topological optical transport and deepens the understanding of Chern insulators with inversion symmetry.

The energy levels and transition rates of promising laser-cooling candidate thorium anion Th^- have been experimentally obtained in the current work. Three new excited states between the bound-bound electric dipole (E1) transition of Th^- are observed now, and their energy levels are determined to be 1,847(13), 3,166.8(59) and 3,666(12) cm^{-1}, respectively. Meanwhile, the lifetime of the upper state of that E1 transition is experimentally determined to be 30(2) microseconds, about 3 times shorter than the previous calculated result 86 microseconds, which makes Th^- the most promising candidate for laser cooling of negative ions. Furthermore, the lifetimes of two other short-lived odd-parity excited states of Th^- are also measured to be 59(4) and 53(3)microseconds, respectively., Comment: 13 pages, 4 figures and 1 supplementary information

We show that the many-body features of graphene band structure and electronic response can be accurately evaluated by applying many-body perturbation theory to a tight-binding (TB) model. In particular, we compare TB results for the optical conductivity with previous ab-initio calculations, showing a nearly perfect agreement both in the low energy region near the Dirac cone ($\sim 100$ meV), and at the higher energies of the {\pi} plasmon ($\sim 5$ eV). A reasonable agreement is reached also for the density-density response at the Brillouin zone corner. With the help of the reduced computational cost of the TB model, we study the effect of self-consistency on the screened interaction (W) and on the quasi-particle corrections, a task that is not yet achievable in ab-initio frameworks. We find that self-consistency is important to reproduce the experimental results on the divergence of the Fermi velocity, while it marginally affects the optical conductivity. Finally, we study the robustness of our results against doping or the introduction of a uniform dielectric environment.

The assembly of molecules to form covalent networks can create varied lattice structures with distinct physical and chemical properties from conventional atomic lattices. Using the smallest stable [5,6]fullerene units as building blocks, various 2D C$_{24}$ networks can be formed with superior stability and strength compared to the recently synthesised monolayer polymeric C$_{60}$. Monolayer C$_{24}$ harnesses the properties of both carbon crystals and fullerene molecules, such as stable chemical bonds, suitable band gaps and large surface area, facilitating photocatalytic water splitting. The electronic band gaps of C$_{24}$ are comparable to TiO$_2$, providing appropriate band edges with sufficient external potential for overall water splitting over the acidic and neutral pH range. Upon photoexcitation, strong solar absorption enabled by strongly bound bright excitons can generate carriers effectively, while the type-II band alignment between C$_{24}$ and other 2D monolayers can separate electrons and holes in individual layers simultaneously. Additionally, the number of surface active sites of C$_{24}$ monolayers are three times more than that of their C$_{60}$ counterparts in a much wider pH range, providing spontaneous reaction pathways for hydrogen evolution reaction. Our work provides insights into materials design using tunable building blocks of fullerene units with tailored functions for energy generation, conversion and storage., Comment: 15 pages, 8 figures, 2 tables

The Jacob's ladder of density functional theory (DFT) proposes the compelling view that by extending the form of successful approximations -- being guided by exact conditions and selected (least empirical) norms -- upper rungs will do better than the lower, thus allowing to balance accuracy and computational effort. Meta-generalized-gradient-approximations (MGGAs) belong to the last rung of the semi-local approximations before hybridization with non-local wave function theories. Among the MGGAs, the Strongly Constrained and Appropriately Normed Approximation (SCAN) greatly improves upon GGAs from the lower rung. But the over magnetized solutions of SCAN make GGAs more reliable for magnetism. Here, we provide a solution that satisfies the most pressing {\em desiderata} for density functional approximations for ferromagnetic, antiferromagnetic and non-collinear states. The approach is available in an implementation in the \textsc{Crystal} electronic structure package.

Photonic integrated circuits require a cladding material on top to prevent any outside interaction with the photonic circuit elements and electromagnetic modes that could cause damage. Mohit et al. proposed selective tuning of the resonance of a cavity by using the mode-index engineering method. However, their work did not consider adding a cladding (upper cladding) material on top of the tuned cavity. In this study, I aim to build upon their work by investigating the impact of depositing cladding material on the frequency distribution of tuned cavities through analytical studies and numerical experiments. I identify crucial calculation parameters and discuss the optimum conditions for high-resolution tuning and large tuning range., Comment: 5 pages, 3 figures. arXiv admin note: substantial text overlap with arXiv:2409.04422