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Thermal Fluctuations in the Phase Structure of the Excitonic Insulator Charge Density Wave State in the Extended Falicov–Kimball Model
摘要： Excitonic insulator (EI) instability accompanied by a charge density wave (CDW) state in the two-dimensional extended Falicov–Kimball model including electron–phonon interaction is investigated by applying the unrestricted Hartree–Fock approximation. Treating both the Coulomb attraction and the electron–phonon coupling on an equal footing, we have derived a set of self-consistent equations, which allows us to determine both the excitonic insulator order parameter and the lattice displacement. The phase structures show us that both the Coulomb interaction and the electron–phonon coupling act together in establishing the EI-CDW state, which typifies either a phononic-CDW or an excitonic-CDW state depending on the competition of the interactions. At a given low temperature, the EI-CDW state is found between two critical values of the Coulomb interaction. The window of the condensation state grows when increasing the electron–phonon coupling. Depending on the temperature and the Coulomb interaction the Bardeen–Cooper–Schrieffer–Bose–Einstein condensation (BCS–BEC) crossover of the EI-CDW state in the systems has been established. Under the effects of phonons, the BCS–BEC crossover deviates to a larger Coulomb interaction while the semimetal–semiconductor transition in the normal state remains.
关键词： semimetal–semiconductor transition,charge density wave,unrestricted Hartree–Fock approximation,Excitonic condensation
更新于2025-09-23 15:23:52
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Photoinduced collective mode, inhomogeneity, and melting in a charge-order system
摘要： We theoretically investigate photoresponses of a correlated electron system upon stimuli of a pulsed laser light. Real-time dynamics of an interacting spinless fermion model on a one-dimensional chain, as a model of charge order (CO), are numerically simulated using the time-dependent Hartree-Fock method. In particular, we discuss the differences between two situations as the initial state: the homogeneous order and the presence of a domain wall, i.e., a kink structure embedded in the CO bulk. Coherent dynamics are seen in the former case: When the frequency of the pump light ωp is varied, along with single particle excitations across the CO gap (ΔCO), the resonantly-excited collective phase mode near ωp ≈ ΔCO/2 efficiently destabilizes CO. In clear contrast, in the latter case, when ωp is tuned at such in-gap frequencies and the intensity of light is sufficiently large, inhomogeneity spreads out from the kink to the bulk region through kink creations. Moreover, even stronger intensity induces the inhomogeneous melting of CO where the CO gap is destroyed.
关键词： photoinduced phase transition,charge order,collective mode,inhomogeneity,time-dependent Hartree-Fock method
更新于2025-09-23 15:23:52
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Path-integral Monte Carlo study of electronic states in quantum dots in an external magnetic field
摘要： We explore the correlated electron states in harmonically confined few-electron quantum dots in an external magnetic field by the path-integral Monte Carlo method for a wide range of the field and the Coulomb interaction strength. Using the phase structure of a preceding unrestricted Hartree-Fock calculation for phase fixing, we find a rich variety of correlated states, often completely different from the prediction of mean-field theory. These are finite temperature results, but sometimes the correlations saturate with decreasing temperature, providing insight into the ground-state properties.
关键词： magnetic field,electron correlations,Hartree-Fock,quantum dots,path-integral Monte Carlo
更新于2025-09-11 14:15:04
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Ionization of hydrogen chloride in few-cycle intense laser pulses
摘要： The single ionization of HCl (X^1Σ^+) molecules in few-cycle intense laser pulses at 800 nm has been studied for laser intensities ranging from 2X 10^13 to 1.4X 10^14 W/cm^2. Total and partial ionization probabilities were computed in the framework of the time-dependent Hartree-Fock theory. The influence of the laser pulse duration and the carrier envelope phase on the HCl ionization was investigated.
关键词： time-dependent Hartree-Fock theory,molecular interactions with photons,single molecular ionization,multiphoton processes,intense-field molecular ionization
更新于2025-09-11 14:15:04
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Non-Markovian pure dephasing in a dielectric excited by a few-cycle laser pulse
摘要： We develop the theory of pure dephasing in a solid exposed to an ultrashort laser pulse beyond the commonly used Markov approximation. This approach takes into account the finite cutoff energy of the bath and can be applied to both many-particle and phonon environments. With numerical simulations performed with the time-dependent Hartree-Fock equations, we investigate how the excitation probability and high-harmonic generation are described by different models of decoherence. It is shown that the time-dependent rates allow for temporally high dephasing to successfully reproduce the main features of high-harmonics spectrum and avoid an overestimation of the charge carrier population after the pulse, which is a common problem of the Markov approximation.
关键词： pure dephasing,time-dependent Hartree-Fock,non-Markovian,ultrashort laser pulse,high-harmonic generation
更新于2025-09-11 14:15:04
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Probing Basis Set Requirements for Calculating Core Ionization and Core Excitation Spectroscopy by the ΔSCF Approach
摘要： We investigate the basis set requirements for calculating properties corresponding to removing core electrons by the ΔSCF approach using Hartree-Fock and density functional theory. Standard contracted basis sets are shown to produce large errors and the improved performance of core-augmented basis sets is traced to the fact that the core-augmenting functions effectively creates an auxiliary set of uncontracted function in the core region. We propose two specific basis sets of double and triple zeta quality based on exponent interpolation of the polarization consistent basis sets, denoted pcX-1 and pcX-2, that display significantly lower basis set errors compared to other alternatives. These are suitable for both non-relativistic and relativistic calculations of the Douglas-Kroll-Hess type, with typical basis set errors of 0.1 and 0.01 eV, respectively, and they can be used in a mixed basis set approach with only a minor degradation in performance. The versions augmented with diffuse functions (aug-pcX-1 and aug-pcX-2) are shown to perform better than other alternatives for X-ray absorption spectroscopy. When used in connection with range-separated hybrid density functional methods and relativistic corrections, the pcX-n basis sets can in favorable cases reproduce experimental results to within a few tenths of an eV.
关键词： basis sets,Hartree-Fock,density functional theory,ΔSCF approach,core ionization,core excitation spectroscopy
更新于2025-09-10 09:29:36
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Structures of the neutral and positively charged forms of the 4,4′,4″-tris(N,N-phenyl-3-methylphenylamino)triphenylamine (m-MTDATA) molecule and its dimer, and charge localization in the corresponding cationic species
摘要： The structures of the 4,4′,4″-tris(N,N-phenyl-3-methylphenylamino)triphenylamine (m-MTDATA) molecule and its dimer in their neutral and positively charged forms were studied by performing quantum-chemical calculations at the Hartree?Fock (HF) and density functional theory (DFT) levels of theory using several exchange-correlation functionals (PBE, PBE0, BHANDHLYP, and M06-HF) with different percentages of HF exchange. It was found that there are at least four possible isomeric structures of m-MTDATA with different (planar or perpendicular) arrangements of the peripheral diphenylamino groups. The charge localization in the monomeric and dimeric cationic species was also determined. The results indicated that the charge on the dimeric cation is localized on the central region or on the side fragment of the cationic part of the dimer, depending on the dimer structure. DFT calculations showed a tendency to overestimate the charge delocalization over the molecule, irrespective of the percentage of HF exchange applied.
关键词： QC calculations,DFT,Hartree?Fock,Charge localization,Dimer
更新于2025-09-10 09:29:36
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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