Influence Of Electron Correlation Research Articles

Influence of electronic correlation on the valley and topological properties of VSiGeP4 monolayer.

Valley is used as a new degree of freedom for information encoding and storage. In this work, the valley and topological properties of the VSiGeP4 monolayer were studied by adjusting the U value based on first-principles calculations. The VSiGeP4 monolayer remains in a ferromagnetic ground state regardless of the change in the U value. The magnetic anisotropy of the VSiGeP4 monolayer is initially in-plane, and then turns out-of-plane with the increase in the U value. Moreover, a topological phase transition is observed in the present VSiGeP4 monolayer with the increase in U value from 0 to 3 eV, i.e., the VSiGeP4 monolayer behaves as a bipolar magnetic semiconductor, a ferrovalley semiconductor, a half-valley metal characteristic, and a quantum anomalous Hall state. The mechanism of the topological phase transition behavior of the VSiGeP4 monolayer was analyzed. It was found that the variation in U values would change the strength of the electronic correlation effect, resulting in the valley and topological properties. In addition, carrier doping was studied to design a valleytronic device using this VSiGeP4 monolayer. By doping 0.05 electrons per f.u., the VSiGeP4 monolayer with a U value of 3 eV exhibits 100% spin polarization. This study indicates that the VSiGeP4 monolayer has potential applications in spintronic, valleytronic, and topological electronic nanodevices.

Impact of electronic correlations on high-pressure iron: insights from time-dependent density functional theory

We present a comprehensive investigation of the electrical and thermal conductivity of iron under high pressures at ambient temperature, employing the real-time formulation of time-dependent density functional theory (RT-TDDFT). Specifically, we examine the influence of a Hubbard correction (+U) to account for strong electron correlations. Our calculations based on RT-TDDFT demonstrate that the evaluated electrical conductivity for both high-pressure body-centered cubic (BCC) and hexagonal close-packed (HCP) iron phases agrees well with experimental data. Furthermore, we explore the anisotropy in the thermal conductivity of HCP iron under high pressure, and our findings are consistent with experimental observations. Interestingly, we find that the incorporation of the +U correction significantly impacts the ground state and linear response properties of iron at pressures below 50 GPa, with its influence diminishing as pressure increases. This study offers valuable insights into the influence of electronic correlations on the electronic transport properties of iron under extreme conditions.

Relativistic Hirshfeld atom refinement of an organo-gold(I) compound.

The main goal of this study is the validation of relativistic Hirshfeld atom refinement (HAR) as implemented in Tonto for high-resolution X-ray diffraction datasets of an organo-gold(I) compound. The influence of the relativistic effects on statistical parameters, geometries and electron density properties was analyzed and compared with the influence of electron correlation and anharmonic atomic motions. Recent work in this field has indicated the importance of relativistic effects in the static electron density distribution of organo-mercury compounds. This study confirms that differences in electron density due to relativistic effects are also of significant magnitude for organo-gold compounds. Relativistic effects dominate not only the core region of the gold atom, but also influence the electron density in the valence and bonding region, which has measurable consequences for the HAR refinement model parameters. To study the effects of anharmonic motion on the electron density distribution, dynamic electron density difference maps were constructed. Unlike relativistic and electron correlation effects, the effects of anharmonic nuclear motion are mostly observed in the core area of the gold atom.

Confined H$$^-$$ ion within a density functional framework

Ground and excited states of a confined negative Hydrogen ion has been pursued under Kohn-Sham density functional approach by invoking a physically motivated work-function-based exchange potential. The exchange-only results are of near Hartree-Fock quality. Local parameterised Wigner-type, and gradient- and Laplacian-dependent non-local Lee-Yang-Parr functionals are chosen to investigate the electron correlation effects. Eigenfunctions and eigenvalues are extracted by using a generalized pseudospectral method obeying Dirichlet boundary condition. Energy values are reported for 1s$^{2}$ ($^{1}$S), 1s2s ($^{3,1}$S) and 1s2p ($^{3,1}$P) states. Performance of the correlation functionals in the context of confinement is examined critically. The present results are in excellent agreement with available literature. Additionally, Shannon entropy and Onicescu energy are offered for ground and low lying singly excited 1s2s ($^{3}$S) and 1s2p ($^{3}$P) states. The influence of electron correlation is more predominant in the weaker confinement limit and it decays with an increase in confinement strength. In essence, energy and some information measures are estimated using a newly formulated density functional strategy.

Direct Observation of Molecular Orbitals Using Synchrotron X-ray Diffraction

The physical properties of molecular crystals are governed by the frontier orbitals of molecules. A molecular orbital, which is formed by superposing the atomic orbitals of constituent elements, has complicated degrees of freedom in the crystal because of the influence of electron correlation and crystal field. Therefore, in general, it is difficult to experimentally observe the whole picture of a frontier orbital. Here, we introduce a new method called “core differential Fourier synthesis” (CDFS) using synchrotron X-ray diffraction to observe the valence electron density in materials. By observing the valence electrons occupied in molecular orbitals, the orbital state can be directly determined in a real space. In this study, we applied the CDFS method to molecular materials such as diamond, C60 fullerene, (MV)I2, and (TMTTF)2X. Our results not only demonstrate the typical orbital states in some materials, but also provide a new method for studying intramolecular degrees of freedom.

Ion energy-loss characteristics and friction in a free-electron gas at warm dense matter and nonideal dense plasma conditions.

We investigate the energy-loss characteristics of an ion in warm dense matter (WDM) and dense plasmas concentrating on the influence of electronic correlations. The basis for our analysis is a recently developed ab initio quantum Monte Carlo- (QMC) based machine learning representation of the static local field correction (LFC) [Dornheim et al., J. Chem. Phys. 151, 194104 (2019)JCPSA60021-960610.1063/1.5123013], which provides an accurate description of the dynamical density response function of the electron gas at the considered parameters. We focus on the polarization-induced stopping power due to free electrons, the friction function, and the straggling rate. In addition, we compute the friction coefficient which constitutes a key quantity for the adequate Langevin dynamics simulation of ions. Considering typical experimental WDM parameters with partially degenerate electrons, we find that the friction coefficient is of the order of γ/ω_{pi}=0.01, where ω_{pi} is the ionic plasma frequency. This analysis is performed by comparing QMC-based data to results from the random-phase approximation (RPA), the Mermin dielectric function, and the Singwi-Tosi-Land-Sjölander (STLS) approximation. It is revealed that the widely used relaxation time approximation (Mermin dielectric function) has severe limitations regarding the description of the energy loss of ions in a correlated partially degenerate electrons gas. Moreover, by comparing QMC-based data with the results obtained using STLS, we find that the ion energy-loss properties are not sensitive to the inaccuracy of the static local field correction (LFC) at large wave numbers, k/k_{F}>2 (with k_{F} being the Fermi wave number), but that a correct description of the static LFC at k/k_{F}≲1.5 is important.

K α1,2α3 and K hα1,2 satellite transition energies and rates for Ar and Ca

SynopsisThe calculations of radiative energies and transition rates for Kα 1,2α3 and Khα1,2 satellite (Mi, M2,3, and N1 spectator holes) lines for Ar and Ca have been carried out by using the GRASP2K and AMBIT codes. The influence of electron correlation on transition rates has been studied.

Modeling the structural distortion and magnetic ground state of the polar lacunar spinel GaV4Se8

The lacunar spinel ${\mathrm{GaV}}_{4}{\mathrm{Se}}_{8}$ is a material whose properties are dominated by tetrahedral clusters of V atoms. The compound is known to undergo a polar distortion to a ground state structure in the $R3m$ space group, and orders ferromagnetically with a relatively small magnetic moment. We develop an understanding into the relationship between crystal structure and magnetic order in this material, and the influence of electron correlations in establishing the observed ground state using first-principles density functional theory (DFT) electronic structure calculations. Because electrons are delocalized within ${\mathrm{V}}_{4}$ clusters but localized between them, the usual approaches to simulate electron correlations---such as the use of the Hubbard $U$ in $\mathrm{DFT}+U$ schemes---do not adequately recreate the experimental ground state. We find instead that the experimental ground state of ${\mathrm{GaV}}_{4}{\mathrm{Se}}_{8}$ is well represented by the random-phase approximation to the correlation energy. Additionally, we find that magnetism and crystal structure are strongly coupled in this material, and only certain arrangements of magnetic moment within a ${\mathrm{V}}_{4}$ cluster can stabilize the observed structural distortion. In combination with the anisotropic, polar nature of the material, the strength of magnetostructural coupling indicates that application of strain could be used to tune the magnetic properties of ${\mathrm{GaV}}_{4}{\mathrm{Se}}_{8}$.

Strong-correlation induced high-mobility electrons in Dirac semimetal of perovskite oxide

Electrons in conventional metals become less mobile under the influence of electron correlation. Contrary to this empirical knowledge, we report here that electrons with the highest mobility ever found in known bulk oxide semiconductors emerge in the strong-correlation regime of the Dirac semimetal of perovskite CaIrO3. The transport measurements reveal that the high mobility exceeding 60,000 cm2V−1s−1 originates from the proximity of the Fermi energy to the Dirac node (ΔE < 10 meV). The calculation based on the density functional theory and the dynamical mean field theory reveals that the energy difference becomes smaller as the system approaches the Mott transition, highlighting a crucial role of correlation effects cooperating with the spin-orbit coupling. The correlation-induced self-tuning of Dirac node enables the quantum limit at a modest magnetic field with a giant magnetoresistance, thus providing an ideal platform to study the novel phenomena of correlated Dirac electron.

Effect of electron correlation in the decomposition of core level binding energy shifts into initial and final state contributions.

The influence of electron correlation into the decomposition of core level binding energy shifts, measured by X-ray photoelectron spectroscopy (XPS), into initial and final effects is analysed for a series of molecules where these effects are noticeable. Moreover, the series of molecules is chosen in such a way that electron delocalization and increasing number of electrons may provide a large screening of the core hole. A detailed analysis shows that the Hartree-Fock decomposition is biased whereas a physically meaningful decomposition is obtained when electron correlation effects are taken into account. The results show that in this case, trends in core level binding energy shifts are driven by initial state effects thus providing further support to the use of these observable quantities to interpret changes in the chemical bond in the neutral molecule rather than on the core ionized cation. Consequences for the theoretical interpretation of XPS data in materials and surface science are discussed.

Influence of electron correlation on the cross section and linear polarization of radiation emitted by electron-impact excitation of Ca+ and Ba+ ions

Calculations of the electron-impact excitation (EIE) of singly charged Ca+ and Ba+ ions and subsequent de-excitation process are performed using a fully relativistic distorted wave (RDW) method. To resolve the discrepancy between previous theory and experiment, careful consideration is given to the generation of the target state wave-functions through the systematic inclusion of electron correlations. It is found that the electron correlation effects play a significant role on the cross section, while the effects on the linear polarization of the emitted radiation are relatively small. Good agreement between our result and experiment is obtained.

Perspective: Coupled cluster theory for atoms and molecules in strong magnetic fields

AbstractIn this perspective, the theoretical treatment of atoms and molecules in strong magnetic fields is discussed. As this is a rather unexplored field, accurate predictions from theory are essential. This is particularly important in the context of astrophysics for the interpretation of observational spectra from white‐dwarf stars that can exhibit magnetic fields up to about 1 B0 ( 235,000 T). A theoretical treatment beyond the pertubation limit requires methods that can deal with finite magnetic fields. Results obtained using coupled cluster (CC) as well as equation‐of‐motion CC theory are presented with a focus on a discussion of the so‐called “perpendicular paramagnetic bonding mechanism” as well as on the influence of electron correlation on total and binding energies. Additionally, the performance of functionals in current density functional theory is discussed. As exact results are completely unknown, highly accurate benchmarks are essential to assess the quality of density functional theory results. Finally, an outlook on future theoretical developments is given.

Optical properties of VO2 films at the phase transition: Influence of substrate and electronic correlations

Thin films of VO2 on different substrates, Al2O3 and SiO2/Si, have been prepared and characterized from room temperature up to 360 K. From the band structure in the rutile metallic phase and in the monoclinic insulating phase, the optical properties are calculated and compared with reflection measurements performed as a function of temperatures. Various interband transitions can be assigned and compared with previous speculations. We extract the parameters of the metallic charge carriers that evolve upon crossing the insulator-to-metal phase transition and find effects by the substrate. The influence of electronic correlations becomes obvious at the phase transition.

Correlation effects in strong-field ionization of heteronuclear diatomic molecules

We develop a time-dependent theory to investigate electron dynamics and photoionization processes of diatomic molecules interacting with strong laser fields including electron-electron correlation effects. We combine the recently formulated time-dependent generalized-active-space configuration interaction theory [D. Hochstuhl and M. Bonitz, Phys. Rev. A 86, 053424 (2012); S. Bauch et al., Phys. Rev. A 90, 062508 (2014)] with a prolate spheroidal basis set including localized orbitals and continuum states to describe the bound electrons and the outgoing photoelectron. As an example, we study the strong-field ionization of the two-center four-electron lithium hydride molecule in different intensity regimes. By using single-cycle pulses, two orientations of the asymmetric heteronuclear molecule are investigated: Li-H, with the electrical field pointing from H to Li, and the opposite case of H-Li. The preferred orientation for ionization is determined and we find a transition from H-Li, for low intensity, to Li-H, for high intensity. The influence of electron correlations is studied at different levels of approximation, and we find a significant change in the preferred orientation. For certain intensity regimes, even an interchange of the preferred configuration is observed, relative to the uncorrelated simulations. Further insight is provided by detailed comparisons of photoelectron angular distributions with and without correlation effects taken into account.

Influence of electron correlations on double-capture process in proton–helium collisions

The first-order correct-boundary Coulomb–Born distorted-wave approximation is used to study the double-electron capture by protons from the ground-state helium atoms at intermediate and high impact energies. The differential double capture cross sections are obtained as a function of the projectile scattering angle and the total cross sections as a function of the impact energy. In the considered range of impact energy, our calculation shows that although the results are not so sensitive to the static inter-electronic correlations in the initial channel, the strong final-state correlations have a large effect on the magnitudes of the double capture cross sections. The calculated differential and integral cross sections are compared with their available experimental values. The comparison shows a good agreement between the present calculations and the measurements. The comparison of the integral cross sections shows that the present approach is compatible with other theories.

Influence of electron correlation on transition energy of gold ions

By using the multi-configuration Dirac–Fock theory and an active space approach, we calculate transition energy, oscillator strength, and transition probability for 4s–4p of Cu-, Zn-, Ga-, and Ge-like gold ions where Breit interaction, quantum electrodynamics, and nuclear-mass corrections have been considered. Our calculation includes valence–valence, core–valence, and core–core correlations, and the contribution of the three kinds of electron correlation effects on transition energy are discussed in detail. Most earlier measurements and calculations focus on the fewer-electrons system of low-Z to medium-Z ions; the purpose of this paper is to verify that core–valence correlation is more important than valence–valence and core–core correlation in a multi-electron system of highly charged high-Z ions.

Lattice dynamics of the rare-earth element samarium

The lattice dynamics of samarium is determined by in situ low-temperature nuclear inelastic scattering on a single crystalline (0001)Sm film, a polycrystalline Sm foil, and by first-principles theory. The ab initio calculated phonon dispersion relations and phonon density of states for the Sm-type structure and the double hexagonal-close-packed (dhcp) lattice, characteristic for light lanthanides, are compared. The dhcp unit cell, which is a factor of 2.24 smaller in height, exhibits more pronounced vibrational anisotropy in comparison to the Sm-type structure. The analysis reveals a minor influence of the spin-orbit coupling in the Sm atom on the lattice dynamics. A broadening of the longitudinal peak, not found in the calculations, suggests the influence of electron correlations on lattice dynamics in metallic samarium.

Effect of electron correlation on high-order harmonic generation in helium model atom

High-order harmonic generation (HHG) of a helium model atom in an intense laser field has been numerically investigated. The influence of electron correlation on HHG is analysed by changing the strength between the electrons. The numerical results show that as the electron interaction strength becomes small, the first ionization energy increases rapidly, which results in the decrease in ionization. So the conversion efficiency of the high harmonic lying in the plateau decreases greatly, while the cutoff harmonic order in the harmonic spectrum increases.

Electron correlation and nuclear charge dependence of parity-violating properties in open-shell diatomic molecules

The scaling of nuclear spin-dependent parity violating effects with increasing nuclear charge $Z$ is discussed in two series of isovalent open-shell diatomic molecules. The parameter $W_\mathrm{a}$ characterising the strength of parity violation in diatomic molecules is calculated in the framework of the zeroth-order regular approximation (ZORA) and found to be in good agreement with the $R(Z) Z^k$ scaling law derived for atoms in which $R(Z)$ represents a relativistic enhancement factor. The influence of electron correlation is studied on the molecular level, with spin-polarisation effects being conveniently accounted for by a previously established approximate relation between the hyperfine coupling tensor and $W_\mathrm{a}$. For high accuracy predictions of parity violating effects in radium fluoride the necessity for systematically improvable correlation calculations is emphasised.

Extended random phase approximation method for atomic excitation energies from correlated and variationally optimized second-order density matrices

Density matrix methods are typically ground state methods. They cannot describe excited states with the same symmetry as the ground state because they rely on energy minimization. The Random Phase Approximation (RPA) is a simple method to derive excitation energies from idempotent first-order density matrices, but the quality of the resulting excitation energies is poor. The quality of the excitation spectrum may be improved by extending the RPA to correlated states. Such an ‘extended RPA’ (ERPA) method depends only on the second-order density matrix (2DM). This work studies the main differences between the ERPA and the RPA – the influence of electron correlation, variational optimality, the ensemble nature of the density matrix and N-representability errors in the input 2DM – by applying the ERPA to exact 2DM’s and variationally optimized 2DM’s. Our findings are relevant for all methods similar to ERPA that determine excitation spectra from low-order density matrices. The inclusion of correlation makes it possible to describe the low-energy excitation spectra of the atoms He–Ne adequately, and the ERPA is thus a good starting point for further refinements, as higher-order excitations should be included to obtain chemical accuracy for many-electron systems. However, the ERPA fails for ensemble density matrices and requires a positive-definite double commutator matrix Ψ0ak†al,H,aj†aiΨ0 to guarantee that the excitation spectrum is real.