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Beyond Born-Oppenheimer treatment on spectroscopic and scattering processes
摘要： We review the formulation of beyond Born-Oppenheimer (BBO) theory based on first principle for the construction of diabatic potential energy surfaces (PESs) both for few important spectroscopic systems, viz., Na3 cluster, NO2 radical as well as scattering process like D+ + H2. The essential theoretical development leading to the BBO equations are thoroughly discussed. It has been found that the above molecular systems posses numerous nonadiabatic interactions that range from Jahn-Teller, Renner-Teller types of conical intersections along with strong pseudo Jahn-Teller couplings between various electronic states. We have calculated the adiabatic PESs and nonadiabatic coupling terms for those systems and subsequently performed adiabatic-to-diabatic transformation to construct smooth, symmetric and continuous diabatic potential energy matrix. Nuclear dynamics has been performed on the diabatic PESs of Na3 and NO2 to simulate the photoelectron spectra that match quite well with the experimentally measured ones. Moreover, we have carried out reactive scattering dynamics on the adiabatic and diabatic surfaces of H+3 system to reproduce experimental cross sections for reactive charge and non-charge transfer processes.
关键词： Beyond Born-Oppenheimer theory,nuclear dynamics,photoelectron spectra,reactive scattering dynamics,conical intersections,Jahn-Teller,diabatic potential energy surfaces,Renner-Teller,nonadiabatic interactions,pseudo Jahn-Teller couplings
更新于2025-09-09 09:28:46
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Direct interaction along light cones at the quantum level
摘要： Here, we point out that interactions with time delay can be described at the quantum level using a multi-time wave function ψ(x1, ..., xN), i.e. a wave function depending on one spacetime variable xi = (ti, xi) per particle. In particular, such a wave function makes it possible to implement direct interaction along light cones (not mediated by fields), as in the Wheeler–Feynman formulation of electrodynamics. Our results are as follows. (1) We derive a covariant two-particle integral equation and discuss it in detail. (2) It is shown how this integral equation (or equivalently, a system of two integro-differential equations) can be understood as defining the time evolution of ψ in a consistent way. (3) We demonstrate that the equation has strong analogies with Wheeler–Feynman electrodynamics and therefore suggests a possible new quantization of that theory. (4) We propose two natural ways how the two-particle equation can be extended to N particles. It is shown that exactly one of them leads to the usual Schr?dinger equation with Coulomb-type pair potentials if time delay effects are neglected.
关键词： quantization of Wheeler–Feynman electrodynamics,integral equations,relativistic quantum theory,integro-differential equations,interaction with time delay,multi-time wave functions,Bethe–Salpeter equation
更新于2025-09-09 09:28:46
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One-particle density matrix polarization susceptibility tensors
摘要： The electric field-induced change in the one-electron density has been expressed as a series of the one-particle density matrix susceptibilities interacting with the spatial distribution of the electric field. The analytic approximate expressions are derived at the Hartree-Fock theory, which serves as a basis for the construction of the generalized model that is designed for an arbitrary form of wavefunction and any type of one-particle density matrix. It is shown that it is possible to accurately predict the changes in the one-electron ground-state density of water molecule in a spatially uniform electric field, as well as in spatially non-uniform electric field distribution generated by point charges. When both linear and quadratic terms with respect to the electric field are accounted for, the electric field-induced polarization energies, dipole moments, and quadrupole moments are quantitatively described by the present theory in electric fields ranging from weak to very strong (0.001–0.07 a.u.). It is believed that the proposed model could open new routes in quantum chemistry for fast and efficient calculations of molecular properties in condensed phases.
关键词： polarization susceptibility tensors,one-particle density matrix,quantum chemistry,Hartree-Fock theory,electric field-induced polarization
更新于2025-09-09 09:28:46
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First-principles study of structural phase transformation and dynamical stability of cubic AlN semiconductors
摘要： Phase transformation and stability of cubic aluminium nitride (AlN) phases such as zinc-blende and rock-salt have been investigated using first-principles calculations based on density functional perturbation theory (DFPT) within quasi-harmonic approximation (QHA). The phonon dispersion relations of both the cubic phases have been calculated at various high-symmetry points of the Brillouin Zone. The pressure and volume dependence of phonon frequencies have been investigated. The application of pressure results in opposite trend of transverse acoustic (TA) phonon frequencies for rock-salt and zinc-blende AlN phases. The TA frequencies found to increase for the former one and decrease for the latter one with the increase in pressure. The dynamical instability results in a volume expansion of rock-salt AlN close to the equilibrium volume of zinc-blende AlN. Phase transformation of these cubic phases is further investigated by computing an equilibrium pressure-temperature phase diagram within QHA. The cubic rock-salt AlN is found to form at high pressures and temperatures than zinc-blende AlN. The temperature dependence of lattice constant and the corresponding volume thermal expansion coefficient of both the cubic phases have been investigated.
关键词： Aluminium nitride,First-principles calculations,Density functional perturbation theory,Quasi-harmonic approximation,Phase transformation,Dynamical stability
更新于2025-09-09 09:28:46
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Performance of DFT for C <sub/>60</sub> Isomerization Energies: A Noticeable Exception to Jacob’s Ladder
摘要： The ability to accurately calculate relative energies of fullerenes is important in many areas of computational nanotechnology. Due to the large size of fullerenes, their relative energies cannot normally be calculated by means of high-level ab initio procedures, and therefore density functional theory (DFT) represents a cost-effective alternative. In an extensive benchmark study, we calculate the electronic energies of eight C60 isomers by means of the high-level G4(MP2) composite procedure. G4(MP2) isomerization energies span a wide range between 307.5–1074.0 kJ mol–1. We use this benchmark data to assess the performance of DFT, double-hybrid DFT (DHDFT), and MP2-based ab initio methods. Surprisingly, functionals from the second and third rungs of Jacob’s Ladder (i.e., GGA and meta-GGA functionals) significantly and systematically outperform hybrid and hybrid-meta-GGA functionals, which occupy higher rungs of Jacob’s Ladder. In addition, DHDFT functionals do not offer a substantial improvement over meta-GGA functionals, with respect to isomerization energies. Overall, the best performing functionals with mean absolute deviations (MADs) below 15.0 kJ mol–1 are (MADs given in parenthesis) the GGA N12 (14.7); meta-GGAs M06-L (10.6), M11-L (10.8), MN15-L (11.9), and TPSS-D3BJ (12.8); and the DHDFT functionals B2T-PLYP (9.3), mPW2-PLYP (9.8), B2K-PLYP (12.1), and B2GP-PLYP (12.3 kJ mol–1). In light of these results, we recommend the use of meta-GGA functionals for the calculation of fullerene isomerization energies. Finally, we show that inclusion of very small percentages of exact Hartree–Fock exchange (3–5%) slightly improves the performance of the GGA and meta-GGA functionals. However, their performance rapidly deteriorates with the inclusion of larger percentages of exact Hartree–Fock exchange.
关键词： Buckminsterfullerene,coupled cluster theory,G4(MP2) theory,density functional theory
更新于2025-09-04 15:30:14
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Game Theory in Molecular Nanosensing System for Rapid Detection of Hg2+ in Aqueous Solutions
摘要： Game theory—the scientific study of interactive, rational decision making—describes the interaction of two or more players from macroscopic organisms to microscopic cellular and subcellular levels. Life based on molecules is the highest and most complex expression of molecular interactions. However, using simple molecules to expand game theory for molecular decision-making remains challenging. Herein, we demonstrate a proof-of-concept molecular game-theoretical system (molecular prisoner’s dilemma) that relies on formation of the thymine–Hg2+–thymine hairpin structure specifically induced by Hg2+ and fluorescence quenching and molecular adsorption capacities of cobalt oxyhydroxide (CoOOH) nanosheets, resulting in fluorescence intensity and distribution change of polythymine oligonucleotide 33-repeat thymines (T33). The “bait” molecule, T33, interacted with two molecular players, CoOOH and Hg2+, in different states (absence = silence and presence = betrayal), regarded as strategies. We created conflicts (sharing or self-interest) of fluorescence distribution of T33, quantifiable in a 2 × 2 payoff matrix. In addition, the molecular game-theoretical-system based on T33 and CoOOH was used for sensing Hg2+ over the range of 20 to 600 nM with the detection limit of 7.94 nM (3σ) and for determination of Hg2+ in pond water. Inspired by the proof-of-concept for molecular game theory, various molecular decision-making systems could be developed, which would help promote molecular information processing and generating novel molecular intelligent decision systems for environmental monitoring and molecular diagnosis and therapy.
关键词： fluorescent sensing,thymine–Hg2+–thymine,game theory,Hg2+,cobalt oxyhydroxide nanosheets
更新于2025-09-04 15:30:14
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The structural and elastic properties of InSb1-xBix alloys
摘要： Based on density functional theory, the structural and elastic properties of InSb1-xBix alloys have been studied using first principle calculations. The generalized gradient approximation in the presence of spin-orbit coupling is utilized to perform the calculations presented in this paper. The calculated lattice constants of InSb1-xBix alloys are in good agreement with the available experimental data. The mechanical stability of these alloys is demonstrated using elastic constants. The ductility and brittleness of these alloys are investigated using both Poisson’s ratio and Pugh’s ratio. Moreover, the anisotropy of InSb1-xBix alloys is studied using the universal index and the 3D representation of Young's modulus. According to the obtained values of Poisson’s ratio, the InSb0.5Bi0.5 and InBi alloys are auxetic materials.
关键词： InSb1-xBix alloys,structural properties,Density functional theory,elastic properties
更新于2025-09-04 15:30:14
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Intrinsic correlation between electronic structure and degradation: from few layers to bulk black phosphorus
摘要： Black phosphorus (BP) has received much attention due to its fascinating properties, such as a high mobility and tunable band gap which covers the band gap lacuna between graphene and transition metal dichalcogenides. However, these advantages have been overshadowed due to the fast degradation of BP in ambient conditions. To overcome this obstacle, the degradation mechanisms should be unveiled with direct observation followed by a thorough analysis. Here, we reveal two sequential degradation processes and layer-dependent degradation rates of BP under dark conditions by scanning Kelvin probe microscopy (SKPM) measurements and theoretical modeling. The layer-dependent degradation is successfully interpreted with the oxidation model based on the Marcus-Gerischer theory (MGT). Under dark conditions, the electron transfer rate from BP to oxygen molecule depends on the number of layers that give different carrier concentrations. The oxidation rate is strongly dependent on the number of layers, and thus carrier concentrations. This suggests the possibility of stability improvement by carrier modulation. This work not only provides a deeper understanding of the degradation mechanism itself but also suggest new strategies for stable BP-based electronics design.
关键词： oxidation model,work function,degradation,black phosphorus,Marcus-Gerischer theory
更新于2025-09-04 15:30:14
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Tuning the Crystal Packing and Semiconductor Electronic Properties of 7,7’-Diazaisoindigo by Side-Chain Length and Halogenation
摘要： In the last years, the 7,7’-diazaisoindigo has emerged as a promising building block for semiconductor materials. In this work, we have studied different electronic properties which can be related to the semiconducting character of a family of 7,7’-diazaisoindigo derivatives. Concretely, we have analyzed the role of halogen substituents and different-length side chains on these properties calculated by means of the Density Functional Theory. In total, sixteen halogenated and non-halogenated diazaisoindigo derivatives were investigated. Four of these compounds were also synthetized and their X-ray structures were employed as starting points for the calculation of crystal structure of the rest of the novel compounds. In general, high electron transfer rate constants and electron mobilites were calculated for the studied 7,7’-diazaisoindigo derivatives, especially for bromine derivatives and compounds with long-side chains. The origin of these high rate constants mainly resides in the strong electronic couplings found for diazaisoindigo crystals in the π-stacking direction.
关键词： 7,7’-diazaisoindigo,side chains,electron mobilities,halogen substituents,Density Functional Theory,semiconductor materials,electron transfer rate constants,π-stacking direction
更新于2025-09-04 15:30:14
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Holevo Capacity of Discrete Weyl Channels
摘要： Holevo capacity is the maximum rate at which a quantum channel can reliably transmit classical information without entanglement. However, calculating the Holevo capacity of arbitrary quantum channels is a nontrivial and computationally expensive task since it requires the numerical optimization over all possible input quantum states. In this paper, we consider discrete Weyl channels (DWCs) and exploit their symmetry properties to model DWC as a classical symmetric channel. We characterize lower and upper bounds on the Holevo capacity of DWCs using simple computational formulae. Then, we provide a sufficient and necessary condition where the upper and lower bounds coincide. The framework in this paper enables us to characterize the exact Holevo capacity for most of the known special cases of DWCs.
关键词： classical symmetric channel,quantum information theory,discrete Weyl channels,Holevo capacity,quantum channel
更新于2025-09-04 15:30:14