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Strain in two-dimensional (2D) materials induces shifts in the visible spectrum due to strained binding energies, an accurate study of which is critical for materials engineering in the design of optoelectronic applications. Different from previous studies that employed computationally demanding theoretical approaches, we present an analytical approach, based on the difference method to calculate the impact of strained binding energy on the optical gap in mono-layer $${\hbox {MoS}}_{2}$$ by exploiting an existing tight binding (TB) and a fractional Coulomb potential model, for strained band gap and binding energy calculation, respectively. The inclusion of strained binding energy, changing at a rate of $$-8.1 \, \hbox {meV}/\bigtriangleup 1\%$$ of biaxial in-plane tensile strain accompanied with a variation of $$-110 \, \hbox {meV}/\bigtriangleup 1\%$$ of strain in the TB band gap, causes the optical gap to alter at a rate of $$-105.3 \, \hbox {meV}/\bigtriangleup 1\%$$ of strain, supported by first-principles calculations and is benchmarked with reported experimental and theoretical values. The effect of strained binding energies causes a blueshift in the optical gap by a correction factor, increasing from $$\approx 0.5\%$$ to $$\approx 12\%$$ , with an increase in equi-biaxial in-plane tensile strain from 1% to 11%, respectively. Furthermore, binding energy sensitivity to strain decreases linearly with a structural change from a mono-layer to a few layers in the 2D regime and saturates in the bulk regime. The presented framework can be used for the calculation of strained binding energies and optical gaps of other 2D materials and thus allows us to tune optical properties of 2D nanomaterials that are sensitive to lattice deformations.

Analytical expressions for the electronic band dispersion were derived using the Green’s function method in the tight binding approximation. A parabolic approximation of the spectrum is proposed, within which the effective carrier mass and quantum capacitance are determined. Using the Koster–Slater and Haldane—Anderson models, the problem of local states of mono- and divacancies are considered. Characteristic phonon frequencies and elastic constants are estimated. The results obtained are compared to the calculation data of other studies.

Density functional tight binding (DFTB) and DFTB-based molecular dynamics (DFTB-MD) were employed to study the crystal structure, electronic properties, intermolecular interactions, and dynamic properties of impurity-containing β-NTO (3-nitro-1,2,4-triazole-5-one) crystals, whose NTO molecules were replaced by different amounts of 1,2.4-triazole-5-one (TO) molecules. As the impurity concentration increased, the stability of crystals decreased and impurity molecules tended to be distributed in the form of aggregates. The band gap of the NTO crystal decreased significantly with the increasing number of impurities and its frontier orbitals were mainly distributed in the local area near impurity molecules. The introduction of impurities enhanced O⋯H and O⋯O interactions, but weakened N⋯O interactions. The decomposition rates of the impurity-containing NTO crystals were faster than that of the ideal crystal during the initial reaction stage and NTO molecules around the impurity molecules began to decompose first. Our results may be useful to reveal the influence of impurities on the properties and decomposition of explosive crystals.

Graphical abstract Molecular dynamics simulations have been performed on a complex in which clusters of boron in the form of molecules of the nanodiamond ortho-carborane (C2B10H12) have been inserted into the four large nonpolar cavities of a nanotube of the right-handed coiled-coil RHCC. The techniques of multi-configurational thermodynamic integration, steered molecular dynamics and umbrella sampling have been combined to investigate the energetics of storage of ortho-carborane in the cavities and to map out the free energy landscape of the RHCC-tetrabrachion-ortho-carboranecomplex along the central channel and along directions transverse to the central channel. The purpose of the study was to explore potential pathways for the diffusion of ortho-carborane between the cavities and the solvent and to assess the stability of the complex as a possible drug delivery system for boron neutron capture therapy (BNCT). The investigation reveals a complex free energy landscape with a multitude of peaks and valleys, all of which can be related to specific architectural elements of the RHCC-nanotube, and the activation barriers for ortho-carborane capture and release support the requirements for rapid cargo uptake coupled with tight binding to the cavities., Molecular dynamics simulations have been performed on a complex in which clusters of boron in the form of molecules of the nanodiamond ortho-carborane (C2B10H12) have been inserted into the four large nonpolar cavities of a nanotube of the right-handed coiled-coil (RHCC)tetrabrachion. The techniques of multi-configurational thermodynamic integration, steered molecular dynamics and umbrella sampling have been combined to investigate the energetics of storage of ortho-carborane in the cavities and to map out the free energy landscape of the RHCC-tetrabrachion-ortho-carboranecomplex along the central channel and along directions transverse to the central channel. The purpose of the study was to explore potential pathways for the diffusion of ortho-carborane between the cavities and the solvent and to assess the stability of the complex as a possible drug delivery system for boron neutron capture therapy (BNCT). The investigation reveals a complex free energy landscape with a multitude of peaks and valleys, all of which can be related to specific architectural elements of the RHCC-nanotube, and the activation barriers for ortho-carborane capture and release support the requirements for rapid cargo uptake coupled with tight binding to the cavities.

The density functional tight binding method was used to explore the energetics, electronic structure, and vibrational spectra of pentaerythritol tetranitrate (PETN) nanoparticles (NPs). The surface energy of the PETN NP is anisotropic and its extra energy decreases with the increase of size. The energy bands of the NPs are significantly expanded and the band gaps are narrowed, thus reducing the stability due to nanometer size effect. The surface of the NP is mainly covered by the NO2 group. The high-energy surface may play a role in triggering chemical decomposition. The vibration frequencies of the PETN NPs present a wider distribution than those of the gas and solid phase PETN, which will increase the probability of energy transfer to the molecules in the system and promote the decomposition of PETN. Our results provide a basic understanding from a molecular perspective to the energy properties of nano explosives.

Considering porous materials as host matrices is an elegant way to enable photoswitching of non-covalently attached organic dyes even in the solid state. By focusing on the resulting optical properties as a function of loading degree and synthesis procedure, the occurring host–guest and guest–guest interactions can be determined and further exploited. In the course of this study, the photochromic behavior of ortho-tetrafluoroazobenzene (tF-AZB) inside flexible DMOF-1 was investigated from these points of view. It was found that depending on the loading degree and temperature, tF-AZB shows varying E/Z ratios and switching efficiency. For systems with low loading, reversible visible light induced isomerization was observed over ten switching cycles: Upon violet light exposure, formation of 100% E isomer was generated, while green light irradiation resulted in ∼60% Z-tF-AZB. Complementary molecular dynamics simulations at DFTB (density functional tight binding)-level revealed changing binding sites for Z-tF-AZB inside DMOF-1. For the E isomer, only low oscillations have been found, which in turn display a rare T-stacking interaction. Although the interaction strengths of the E and Z isomers with DMOF-1 are in the same range, the different mobility of both isomers due to varying binding sites explains the preference of the E isomer even upon green light exposure.

Bulk-heterojunction (BHJ) organic solar cells (OSCs) exhibit ultrafast charge separation (UCS) which enables lower geminate charge recombination and high internal quantum efficiency. Unravelling why UCS occurs in BHJ-OSCs is important for the exploration of devices in future, however it is still far from clear. In this work, we build a multichain tight-binding model to study the conditions for realizing UCS. We propose that two conditions are important: (i) the BHJ-OSC has a morphology with donor and acceptor molecules being individually aggregated; (ii) the ratio of the donor/acceptor interfacial coupling to the internal donor/donor and acceptor/acceptor coupling should be smaller than a threshold. In addition, we suggest that increasing the donor/acceptor energetic offset will boost the UCS efficiency. As a fundamental theoretical analysis on the underlying mechanism of UCS, our work provides design rules for optimizing high-performance BHJ OSCs.

Atomically thin two-dimensional molybdenum disulfide (MoS2) is well known for its excellent lubrication characteristics and is usually used as a solid lubricant in diverse micro/nanoelectromechanical systems (MEMS/NEMS). The friction on atomically thin MoS2 deposited on a SiO2/Si substrate is reduced almost five times to achieve an ultra-low friction state (coefficient of friction nearly 0.0045) by rubbing the surface with an AFM tip under the electric field. The electric field leads to a shift and accumulation of charges at the interface between MoS2 and the SiO2/Si substrate. Then, electronic tight-binding with high interfacial bonding strength is experimentally found by the charges transferring during the rubbing process. The ultra-low friction state of atomically thin MoS2 could attribute to the electronic tight-binding between MoS2 and the SiO2/Si substrate, which suppresses the atomic-scale deformation and limits the local pinning capability of MoS2. The ultra-low friction state on atomically thin MoS2 is patterned further by controllably regulating position, time, and electric field during the rubbing process. This approach can provide an additional channel to achieve ultra-low friction on MoS2 related two-dimensional materials with semiconductor properties. The nanopatterning of ultra-low friction could promote and expand engineering applications of MoS2 as lubricants in various MEMS/NEMS with nano-scale components.

Ligand-free Cs4PbBr6 particles of sub-micron dimensions were fabricated by a simple tip-sonication method showing 85.1% photoluminescence quantum yield (PLQY). Cs4PbBr6 microcrystals can be grown under saturated vapor pressure with the particles as nucleation units. Surface traps are the main defects in the Cs4PbBr6 particles with smaller size, whereas bulk defects dominate in the larger microcrystals. The intensity of the low energy PL peak increases with excitation intensity at low temperature, which can be assigned to band filling and charge transfer effects. The exciton binding energy of Cs4PbBr6 particles is 180 meV which is almost twice that of the Cs4PbBr6 microcrystals. Such tight binding of the excitons facilitates exciton radiative recombination. In addition, the long excited-state lifetime of the Cs4PbBr6 particles contributes to the higher PLQY compared to that of comparable microcrystals. Time-resolved emission microscopy images clearly indicate different recombination kinetics in the ordered and defect regions, which is hidden in ensemble measurements. This strongly suggests that surface trap states are the main reason for the high-efficiency photoluminescence of the intrinsic Cs4PbBr6 particles investigated here, although both surface and bulk traps can emit light.

In this paper, the performance of GaAs and GaSb based sub-10 nm double-gate junctionless metal-oxide-semiconductor field-effect transistors (DG-JLMOSFETs) have been studied for high-performance switching applications. The quantum transmitting boundary method (QTBM) has been considered for electron transport, and the band structures are accounted for sp3d5s* tight-binding modeling. The channel thickness, tch is varied from 1.7 to 4.7 nm to evaluate the device figure of merits (FOMs). The thinner channel’s device shows a lower OFF-state current, while the ticker channel device allows a higher ON-state current. The threshold voltage is approximately 0.4 V for GaAs DG-JLMOSFETs with tch = 1.7 nm, whereas it reduces to ~0.05 V for that of tch = 4.7 nm. Similar characteristics have been shown in GaSb devices. Besides, a significant impact of tch on the subthreshold swing (SS) and drain-induced barrier lowering (DIBL) is found in GaSb DG-JLMOSFETs compared with those of GaAs devices. The devices show a higher leakage-power dissipation in both channel materials and low-intrinsic delay for thicker tch due to a substantial amount of energy drop. The above results indicate that III-V-based DG-JLMOSFETs are very promising for next-generation high-performance switching technology.

International audience; Using the tight binding description of the electronic structure of graphene and a time-dependent quantum approach, we address the vibrational excitation of molecules in the near field of a graphene nanoantenna. The possibility of tuning the graphene plasmon frequency by electrostatic doping allows an efficient resonant excitation of the infrared (IR)-active vibrational modes via the coupling between the molecular dipole and plasmon near field. We show that for the carbon monoxide CO molecules placed in the gap of a dimer antenna formed by the 20 nm size graphene patches, an excitation of the υ=1←0 transition leads to a distinct molecular signature in the IR absorption spectrum of the system. A very small number of molecules down to a single molecule placed in the antenna gap can thus be detected. Along with IR-active vibrations, the inhomogeneity of the plasmonic near field allows vibrational excitation of IR-inactive molecules via molecular quadrupole. The resonant excitation of the N2 molecule vibration is thus observed in the calculated absorption spectra, albeit the molecule signature is essentially smaller than for the CO molecule. Obtained with molecules described on the ab initio quantum chemistry level, our results provide quantitative insights into the performance of graphene nanoflakes and their dimers for molecular sensing.

Combining a computationally efficient and affordable molecular dynamics approach, based on atom-centered density matrix propagation scheme, with the density functional tight binding semiempirical quantum mechanics, we study the vibrational dynamics of a single molecule at series of finite temperatures, spanning quite wide range. Data generated by molecular dynamics simulations are further analyzed and processed using time series analytic methods, based on correlation functions formalism, leading to both vibrational density of states spectra and infrared absorption spectra at finite temperatures. The temperature-induced dynamics in structural intramolecular parameters is correlated to the observed changes in the spectral regions relevant to molecular detection. In particular, we consider a case when an intramolecular X-H stretching vibrational states are notably dependent on the intramolecular torsional degree of freedom, the dynamics of which is, on the other hand, strongly temperature-dependent.

The molecular speciation of aluminum (Al3+) in alkaline solutions is fundamental to its precipitation chemistry within a number of industrial applications that include ore refinement and industrial processing of Al wastes. Under these conditions, Al3+ is predominantly Al(OH)4-, while at high [Al3+] dimeric species are also known to form. To date, the mechanism of dimer formation remains unclear and is likely influenced by complex ion···ion interactions. In the present work, we investigate a suite of potential dimerization pathways and the role of ion pairing on energetics using static DFT calculations and DFT and density functional tight binding molecular dynamics. Specific cation effects imparted by the background electrolyte cations Na+, Li+, and K+ have been examined. Our simulations predict that, when the Al species are ion-paired with either cation, the formation of the oxo-bridged Al2O(OH)62- is favored with respect to the dihydroxo-bridged Al2(OH)82-, in agreement with previous spectroscopic work. The formation of both dimers first proceeds by bridging of two monomeric units via one hydroxo ligand, leading to a labile Al2(OH)82- isomer. The effect of contact ion pairing of Li+ and K+ on the dimerization energetics is distinctly more favorable than that of Na+, which may have an effect on further oligomerization.

High-order charge transfer is incorporated into the fragment molecular orbital (FMO) method using a charge transfer state with fractional charges. This state is used for a partition analysis of properties based on segments that may be different from fragments in FMO. The partition analysis is also formulated for calculations without fragmentation. All development in this work is limited to density-functional tight-binding. The analysis is applied to a water cluster, crambin (PDB: 1CBN), and two complexes of Trp-cage (1L2Y) with ligands. The contributions of functional groups in ligands are obtained, providing useful information for drug discovery.

The structural and vibration properties of the (√3 × √3)R30°–Cr adsorption structure on the Cu(111) surface and the Cu(111)–(√3 × √3)R30°–Cr two-dimensional alloy incorporated into the S – 1 substrate layer are studied using the tight binding approximation. Surface relaxation is discussed along with the dispersion of surface phonons and the local density of vibration states of adatoms and substrate atoms. It has been demonstrated that the presence of chromium atoms modifies the structural and vibration characteristics of the substrate and leads to the appearance of new phonon states in it. The analysis of the entire set of data has shown that the Cu(111)–(√3 × √3)R30°–Cr subsurface two-dimensional alloy is a more stable configuration.

We present an efficient approach to precisely simulate tight binding models with optical lattices, based on programmable digital-micromirror-device (DMD) techniques. Our approach consists of a subroutine of Wegner-flow enabled precise extraction of a tight-binding model for a given optical potential, and a reverse engineering step of adjusting the potential for a targeting model, for both of which we develop classical algorithms to achieve high precision and high efficiency. With renormalization of Wannier functions and high band effects systematically calibrated in our protocol, we show the tight-binding models with programmable onsite energies and tunnelings can be precisely simulated with optical lattices integrated with the DMD techniques. With numerical simulation, we demonstrate that our approach would facilitate quantum simulation of localization physics with unprecedented programmability and atom-based boson sampling for illustration of quantum computational advantage. We expect this approach would pave a way towards large-scale and precise programmable quantum simulations based on optical lattices., Comment: 10 pages, 5 figures

Using the potentials, generated by a tight binding approximation, the equilibrium atomic structure and the phonon spectra of Cr and Ni thin films (one monolayer) deposited on the Cu (111) surface are calculated. The atomic relaxation, the vibrational state density distribution on the Cr, Ni and substrate atoms and the polarization of vibrational modes are considered. The change in the phonon spectrum during film deposition and the segregation of Cu atoms on the film surface are discussed. It is shown that mixing of the Cr and Ni atomic vibrations with those of the substrate takes place in the entire frequency range, resulting in a frequency shift of the vibrational modes of the substrate and the formation of new vibrational states not typical for a clean surface. The Cu/Cr/Cu and Cu/Ni/Cu structures are found to be more stable dynamically.

The design and fabrication of robust metallic states in graphene nanoribbons (GNRs) is a significant challenge since lateral quantum confinement and many-electron interactions tend to induce electronic band gaps when graphene is patterned at nanometer length scales. Recent developments in bottom-up synthesis have enabled the design and characterization of atomically-precise GNRs, but strategies for realizing GNR metallicity have been elusive. Here we demonstrate a general technique for inducing metallicity in GNRs by inserting a symmetric superlattice of zero-energy modes into otherwise semiconducting GNRs. We verify the resulting metallicity using scanning tunneling spectroscopy as well as first-principles density-functional theory and tight binding calculations. Our results reveal that the metallic bandwidth in GNRs can be tuned over a wide range by controlling the overlap of zero-mode wavefunctions through intentional sublattice symmetry-breaking., Comment: The first three authors listed contributed equally

A key starting assumption in many classical interatomic potential models for materials is a site energy decomposition of the potential energy surface into contributions that only depend on a small neighbourhood. Under a natural stability condition, we construct such a spatial decomposition for self-consistent tight binding models, extending recent results for linear tight binding models to the non-linear setting., Comment: 15 pages

The computer simulation method was used to examine condensation of 90124 Cu and Au atoms from the gas phase. To analyze the synthesis processes, there were selected chemical compositions Cu3Au, Cu-Au, Cu90Au10 and Cu60Au40 being cooled with liquid nitrogen during the condensation. The undertaken simulation showed that the increase in the percentage of gold atoms in the initial couple decreases the number of clusters of a relatively large size. Moreover, the analysis of the external view and the structure of Cu-Au nanoparticles of various chemical composition allowed us to conclude that a large number of binary nanoparticles were of an icosahedral structure.

In this work a number of computational methods have been applied to study the adsorption of dimethylmercury (DMM) on the (ZnO)6 cluster and the influences of the supports (MgO, SBA-15) and external ions (Cl−, OH−) on the adsorption process: the energy and electronic properties were calculated using Geometry, Frequency, Noncovalent, eXtended Tight Binding method; global minimum was found by using the Artificial Bee Colony algorithm; the Growing String Method was used to scan the potential energy surface to determine the transition states, and the stability of the adsorption products was investigated via molecular dynamic simulations. The calculated results show that the interaction between (ZnO)6 and DMM are both kinetically and thermodynamically favorable. The strong chemisorption of DMM on the (ZnO)6/MgO and (ZnO)6/SBA-15 is the consequence of the interaction between (ZnO)6 cluster and the supports. The higher adsorption affinity toward DMM of (ZnO)6/MgO, compared to (ZnO)6/SBA-15, is due to the synergistic effect of MgO with (ZnO)6. However, in the OH− ion environment, (ZnO)6/SBA-15, reversely, seemed to be a better adsorbent for DMM molecules.

The energetics, electronic features, and vibrational properties of a series of triamino-trinitrobenzene (TATB) nanoparticles (NPs) were investigated by density functional theory (DFT) with density functional tight binding (DFTB) methods. The surface energies, enthalpy of sublimation, and melt point for different TATB NPs were compared. The surface-related electronic states in the NPs narrower the energy gap and provide the active sites at surfaces. The vibrational properties of the TATB NPs were carefully compared with those of the gaseous and solid phase TATB. The correlation between the surface molecules in the TATB NPs and initial decomposition was discussed. Our results provide insights into the comprehensive understandings of high activity of nano explosives at the atomic and electronic levels.

Theoretical description of liquids, especially liquid water, is an ongoing subject with important implications in various domains such as homogeneous catalysis; solvation of molecular, ionic, and biomolecular species; and reactivity. Various formalisms exist to describe liquids, each one displaying its own balance between accuracy and computational cost that defines its range of applications. The present article revisits the ability of the density-functional-based tight-binding (SCC-DFTB) approach to model liquids by focusing on liquid water and liquid benzene under ambient conditions. To do so, we benchmark a recent correction for the SCC-DFTB atomic charges that allows for a drastic improvement of the pair radial distribution functions of liquid water as compared to both experimental data and density-functional theory results performed in the generalized-gradient approximation. We also report the coupling of the deMonNano and i-PI codes to perform path-integral molecular dynamics. This allows us to rationalize the impact of nuclear quantum effects on the SCC-DFTB description of liquid water. This study evidences the rather good ability of SCC-DFTB to describe liquid water and liquid benzene. As the first example of application, we also present results for a benzene molecule solvated in water with the perspectives of further studies devoted to solvent/water interfaces.

Understanding the influence of adsorption sites to the electronic properties of adsorbed molecules on two-dimensional (2D) ultrathin insulator is of essential importance for future organic-inorganic hybrid nanodevices. Here, the adsorption and electronic states of manganese phthalocyanine (MnPc) on a single layer of hexagonal boron nitride (h-BN) have been comprehensively studied by low-temperature scanning tunneling microscopy/spectroscopy and tight binding calculations. The frontier orbitals of the MnPc can change drastically by reversible manipulation of individual MnPc molecules onto and away from the single atomic vacancies at the h-BN surface. Particularly, the change of the molecular electronic configuration can be controlled depending on whether the atomic vacancy is below the metal center or the ligand of the MnPc. These findings give new insight into defect-engineering of the organic-inorganic hybrid nanodevices down to submolecular level.

Controlling carbon emissions is an effective way to mitigate the greenhouse effect. According to the primary energy consumption of China, chemical looping combustion (CLC) using coal as the fuel ha...

[ The study of transmission probability and IV chracteristics of a G4 molecule ] In this era, there have been many theoretical and experimental studies conducted to enhance technological development. The development of technology continues to grow rapidly with electronic components that are getting smaller towards nano. Nanotechnology is becoming increasingly interesting because it can be created through DNA that is found in either the human body or other living things. This research was conducted to study DNA transport properties by calculating transmission probabilities and I-V characteristics. The DNA studied is DNA that has been modified consisting of 4 guanine bases arranged stacked to form a square called G4-DNA. G4-DNA is composed by having 32 base pairs and connected by electrodes at the end. The transport properties of G4-DNA were studied using the Hamiltonian tight binding approach. Transmission probability is calculated using the method of the Green Function Hamiltonian to determine the possibility of electrons flowing along the DNA pathway. This transmission probability is used in determining the I-V Characteristics based on the Landauer Buttiker formula. The result s are obtained that the electron transport process along the G4-DNA molecule is an increase in current to high voltage. The effects of I-V characteristics are seen by affecting the twisting motion frequency up to 5.12 meV which is a significant increase in current. The results of this study can provide information about the characteristics of DNA that can be applied in the future in manufacture of nanotechnology device .

We have examined the electronic structure evolution in transition metal dichalcogenides MX2 where M = Mo, W and X = S, Se, and Te. These are generally referred to as van der Waals materials on the one hand, yet one has band gap changes as large as 0.6 eV with thickness in some instances. This does not seem to be consistent with a description where the dominant interactions are van der Waals interactions. Mapping onto a tight binding model allows us to quantify the electronic structure changes, which are found to be dictated solely by interlayer hopping interactions. Different environments that an atom encounters could change the Madelung potential and therefore the onsite energies. This could happen while going from the monolayer to the bilayer as well as in cases where the stackings are different from what is found in 2H structures. These effects are quantitatively found to be negligible, enabling us to quantify the thickness-dependent electronic structure changes as arising from interlayer interactions alone.

Graphyne sheets and nanotubes (GyNTs) are known as novel low-dimensional, i.e., two-dimensional (2D) and one-dimensional (1D), semiconducting carbon allotropes that can be used in nanoelectronics and therefore merit fundamental investigation. Among such materials, attention is currently focused on γ-graphyne-1, a member of the graphyne family that exhibits a maximum cohesive energy of −8.37 eV and chemical stabilityhas been focused. In this research density functional tight binding (DFTB) method in the investigation of electrical property under geometrical variation is reported and a detailed description of electrical as well as stability properties for γ-graphyne-1 in uniform strain is illustrated. It is concluded that the γ-graphyne-1 family of materials exhibit semiconducting properties with large bandgap values from 1.34 eV for the sheet structure to 1.93 eV for (3,0) armchair γ-graphyne-1 nanotubes. The γ-graphyne-1 family also displays elastic properties, enabling the modulation of the bandgap and engineering of the effective mass using homogeneous strain. These properties, along with the nonmetallic behavior of GyNTs, make them perfect materials for the design of novel electronic devices.

Sublimation enthalpies of alkane-α,ω-diamines exhibit an odd-even pattern within their homologous series. First-principles calculations coupled with the quasi-harmonic approximation for crystals and with the conformation mixing model for the ideal gas are used to explain this phenomenon from the theoretical point of view. Crystals of the odd and even alkane-α,ω-diamines distinctly differ in their packing motifs. However, first-principles calculations indicate that it is a delicate interplay of the cohesive forces, phonons, molecular vibrations and conformational equilibrium which governs the odd-even pattern of the sublimation enthalpies within the homologous series. High molecular flexibility of the alkane-α,ω-diamines predetermines higher sensitivity of the computational model to the quality of the optimized geometries and relative conformational energies. Performance of high-throughput computational methods, such as the density functional tight binding (DFTB, GFN2-xTB) and the explicitly correlated dispersion-corrected Møller-Plesset perturbative method (MP2C-F12), are benchmarked against the consistent state-of-the-art calculations of conformational energies and interaction energies, respectively.

We studied the electronic band structure and corresponding local density of states of low-index fcc Ag surfaces (100), (110), and (111) by using the empirical tight-binding method in the framework of the Surface Green’s Function Matching formalism. The energy values for different surface and resonance states are reported and a comparison with the available experimental and theoretical data is also done.

The first density functional tight-binding (DFTB) parameters for uranium, oxygen, and hydrogen chemistry are reported, which enable quantum molecular dynamics simulations that will be instrumental in understanding actinide speciation, reaction mechanisms, and kinetics. These parameters were fitted to atomization energies and forces obtained from density functional theory with a training set of small molecules that includes various oxidation states. The energetic results with these DFTB parameters for various reactions of hydration, hydrolysis, dimerization, and isomerization demonstrate that the DFTB method can qualitatively capture the correct chemistry with a small systematic deviation from the density functional theory reference values. Structural results on the molecules not in the training set, including dimers, show generally good agreement with the reference and demonstrate the transferability of these first DFTB parameters for uranium chemistry.

Three-dimensional porous carbon materials play a significant role in gas separation and energy storage. However, their low performances in energy storage hamper their applications. Herein, we propose a new possible category of carbon honeycomb (CHC), i.e. CHCs with asymmetrical channels (denoted as asymmetrical CHCs), to increase their performance. As an example, by cross-linking graphene sheet with sp3–hybridized carbon chains, we prepare a new 3D porous asymmetrical CHC, i.e. bco-C24. It is dynamically, thermally, and mechanically stable. Our first-principles calculations and tight binding results demonstrate that it possesses a significant electronic band structure of Dirac nodal lines, which are ascribed to the px and py orbitals of α carbon atoms in the graphene ribbons that have both α and β carbon atoms. It provides high carrier mobility between 7.98 × 105 and 9.99 × 105 m/s. It has high theoretical capacities (743.8/495.9/991.8/743.8 mA h/g), low diffusion barriers (0.077/0.032/0.117/0.169 eV), low average voltages, and negligible volume changes for Na/K/Ca/Li-ion batteries. This study not only constructs a new concept of asymmetrical CHCs and provides a strategy of cross-linking graphene sheets to create its sample structures, but also suggests new carriers for ion storage in the superior next generation metal-ion battery anodes.

We use density functional tight binding (DFTB) molecular dynamics (MD) simulations to determine the reaction rates of nitromethane CH3NO2 (NM) under high pressure (P=14--28 GPa), and temperature (1...

A spin-flip time-dependent density functional tight-binding (SF-TDDFTB) method is developed that describes target states as spin-flipping excitation from a high-spin reference state obtained by the spin-restricted open shell treatment. Furthermore, the SF-TDDFTB formulation is extended to long-range correction (LC), denoted as SF-TDLCDFTB. The LC technique corrects the overdelocalization of electron density in systems such as charge-transfer systems, which is typically found in conventional DFTB calculations as well as density functional theory calculations using pure functionals. The numerical assessment of the SF-TDDFTB method shows smooth potential curves for the bond dissociation of hydrogen fluoride and the double-bond rotation of ethylene and the double-cone shape of H3 as the simplest degenerate systems. In addition, numerical assessments of SF-TDDFTB and SF-TDLCDFTB for 39 S0 /S1 minimum energy conical intersection (MECI) structures are performed. The SF-TDDFTB and SF-TDLCDFTB methods drastically reduce the computational cost with accuracy for MECI structures compared with SF-TDDFT.

The structural, optical and electronic properties of different-sized pure as well as transition metals doped TiO2 quantum dots were investigated using density functional tight binding (DFTB) methods. The self-consistent charge density functional tight binding theory (SCC-DFTB) was used to model the TiO2 quantum dots (QDs) of increasing size up to 3.03 nm. The size dependence of density of states, position of molecular orbitals, and gap between highest orbital molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) of the QDs were studied. It appeared that, when the size of QDs approaches 3.03 nm, the energy gap narrowed down due to quantum confinement effects. The QD Ti27O54 was doped with 3d transition metals to further explore the possibility of tailoring the properties. The dopants introduced 3d impurity gap states which opens the opportunity to modify the band gap or positions of principal bands. The position of a shifted Fermi level was monitored to explore the changes in conductivity and n- or p-type behaviors of the doped QDs. It was observed that TiO2 QDs doped with V and Cr showed the n-type behavior while those doped with Sc, Mn and Fe showed p-type behavior. The findings are helpful to enhance the photocurrent efficiency of dye-sensitized solar cells and use the materials in electronic and optoelectronic properties.

In this theoretical study, the band structure of MoS2 monolayer was initially numerically calculated using an 11-band tight-binding Hamiltonian model. Then, the contributions of d and p orbitals on the density of states (DOS), electronic heat capacity (EHC), and Pauli magnetic susceptibility (PMS) of the system were investigated based on the mentioned model and the Green’s function method. Also, the temperature dependence of the EHC and PMS is compared for the d and the p orbitals. An obvious gap was observed in the band structure and DOS of the MoS2 monolayer system, which is in good agreement with previous works. Moreover, due to the orbital overlap, Van Hove singularities appear. Then, as a result of this, a crossover occurs in the curves of PMS, which are divided into a low- and high-temperature region. Further, a Schottky anomaly is observed in the EHC curves. Overall, in this paper, we have introduced a method to investigate the electronic properties of $${{ {MoS}}}_{2}$$ monolayer that can be applied to other monolayer dichalcogenides.

Phonons crucially impact a variety of properties of organic semiconductor materials. For instance, charge- and heat transport depend on low-frequency phonons, while for other properties, such as the free energy, especially high-frequency phonons count. For all these quantities one needs to know the entire phonon band structure, whose simulation becomes exceedingly expensive for more complex systems when using methods like dispersion-corrected density functional theory (DFT). Therefore, in the present contribution we evaluate the performance of more approximate methodologies, including density functional tight binding (DFTB) and a pool of force fields (FF) of varying complexity and sophistication. Beyond merely comparing phonon band structures, we also critically evaluate to what extent derived quantities, like temperature-dependent heat capacities, mean squared thermal displacements and temperature-dependent free energies are impacted by shortcomings in the description of the phonon bands. As a benchmark system, we choose (deuterated) naphthalene, as the only organic semiconductor material for which to date experimental phonon band structures are available in the literature. Overall, the best performance amongst the approximate methodologies is observed for a system-specifically parametrized second-generation force field. Interestingly, in the low-frequency regime also force fields with a rather simplistic model for the bonding interactions (like the General Amber Force Field) perform rather well. As far as the tested DFTB parametrization is concerned, we obtain a significant underestimation of the unit cell volume resulting in a pronounced overestimation of the phonon energies in the low frequency region. This cannot be mended by relying on the DFT-calculated unit cell, since with this unit cell the DFTB phonon frequencies significantly underestimate the experiments., Supporting Information is available free of charge at https://pubs.acs.org/doi/abs/10.1021/acs.jctc.0c00119