A new ATSP2K module is presented for evaluating the electron density function of any multiconfiguration Hartree-Fock or configuration interaction wave function in the non relativistic or relativistic Breit-Pauli approximation. It is first stressed that the density function is not a priori spherically symmetric in the general open shell case. Ways of building it as a spherical symmetric function are discussed, from which the radial electron density function emerges. This function is written in second quantized coupled tensorial form for exploring the atomic spherical symmetry. The calculation of its expectation value is performed using the angular momentum theory in orbital, spin, and quasispin spaces, adopting a generalized graphical technique. The natural orbitals are evaluated from the diagonalization of the density matrix.
We present the fully general time-dependent multiconfiguration self-consistent-field method to describe the dynamics of a system consisting of arbitrary different kinds and numbers of interacting fermions and bosons. The total wave function is expressed as a superposition of different configurations constructed from time-dependent spin-orbitals prepared for each particle kind. We derive equations of motion followed by configuration-interaction (CI) coefficients and spin-orbitals for general, not restricted to full-CI, configuration spaces. The present method provides a flexible framework for t…
The multiconfiguration Dirac-Hartree-Fock (MCDHF) method has been employed to calculate atomic electric dipole moments (EDM) of 225^Ra, 199^Hg, and 171^Yb. For the calculations of the matrix elements we extended the relativistic atomic structure package GRASP2K. The extension includes programs to evaluate matrix elements of (P, T)-odd e-N tensor-pseudotensor and pseudoscalar-scalar interactions, the atomic electric dipole interaction, the nuclear Schiff moment, and the interaction of the electron electric dipole moment with nuclear magnetic moments. The interelectronic interactions were accoun…
We present an implementation of a time-dependent multiconfiguration self-consistent-field (TD-MCSCF) method [R. Anzaki et al., Phys. Chem. Chem. Phys. 19, 22008 (2017)] with the full configuration interaction expansion for coupled electron-nuclear dynamics in diatomic molecules subject to a strong laser field. In this method, the total wave function is expressed as a superposition of different configurations constructed from time-dependent electronic Slater determinants and time-dependent orthonormal nuclear basis functions. The primitive basis functions of nuclei and electrons are strictly in…
The multiconfiguration Dirac-Hartree-Fock (MCDHF) model has been employed to calculate the expectation values for the hyperfine splittings of the 5d96s2 2D3/2 and 5d96s2 2D5/2 levels of atomic gold. One-, two-, and three-body electron correlation effects involving all 79 electrons have been included in a systematic manner. The approximation employed in this study is equivalent to a Complete Active Space (CAS) approach. Calculated electric field gradients, together with experimental values of the electric quadrupole hyperfine structure constants, allow us to extract a nuclear electric quadrupol…
The electron-ion recombination rate coefficient for Si IV forming Si III was measured at the heavy-ion storage-ring TSR. The experimental electron-ion collision energy range of 0-186 eV encompassed the 2p(6) nl n'l' dielectronic recombination (DR) resonances associated with 3s to nl core excitations, 2s 2p(6) 3s nl n'l' resonances associated with 2s to nl (n=3,4) core excitations, and 2p(5) 3s nl n'l' resonances associated with 2p to nl (n=3,...,infinity) core excitations. The experimental DR results are compared with theoretical calculations using the multiconfiguration Dirac-Fock (MCDF) meth…
The time-dependent multiconfiguration self-consistent-field method based on the occupation-restricted multiple active space model is proposed (TD-ORMAS) for multielectron dynamics in intense laser fields. Extending the previously proposed time-dependent complete-active-space self-consistent-field method [TD-CASSCF; Phys. Rev. A, {\bf 88}, 023402 (2013)], which divides the occupied orbitals into core and active orbitals, the TD-ORMAS method {\it further} subdivides the active orbitals into an arbitrary number of subgroups, and poses the {\it occupation restriction} by giving the minimum and max…
We theoretically study high-harmonic generation (HHG) from transition metal elements Mn and Mn$^+$, using full-dimensional, all-electron, first-principles simulations. The HHG spectra calculated with the time-dependent complete-active-space self-consistent-field (TD-CASSCF) and occupation-restricted multiple-active-space (TD-ORMAS) methods exhibit a prominent peak at $\sim 50$ eV, successfully reproducing resonant enhancement observed in previous experiments [R.A. Ganeev \textit{et al.}, Opt. Express \textbf{20}, 25239 (2012)]. Artificially freezing $3p$ orbitals in simulations results in its …
The fully relativistic multiconfiguration Dirac--Hartree--Fock method is used to compute excitation energies and lifetimes for the 143 lowest states of the $3s^23p^3$, $3s3p^4$, $3s^23p^23d$, $3s3p^33d$, $3p^5$, $3s^23p3d^2$ configurations in P-like ions from Cr X to Zn XVI. Multipole (E1, M1, E2, M2) transition rates, line strengths, oscillator strengths, and branching fractions among these states are also given. Valence-valence and core-valence electron correlation effects are systematically accounted for using large basis function expansions. Computed excitation energies are compared with t…
State-of-the-art relativistic multiconfiguration Dirac-Hartree-Fock calculations have been performed to evaluate the electronic field and mass isotope shift factors of the Cu~I resonance line at $λ= 324.8$~nm. A linear correlation between the mass factors and the transition energy is found for elaborate correlation models, allowing extrapolation to the observed frequency limit. The relativistic corrections to the recoil operator reduces the transition mass factor by 5~\%.
The multiconfiguration Dirac-Hartree-Fock method is applied to study the electron affinities of At and its homologous elements Cl, Br, and I. Our method of calculation is validated through the comparison with the available experimental electron affinities of Cl, Br, I, and other theoretical values. The agreement between our predicted electron affinities and the available experimental values for Cl, Br, and I is within 0.2%, which is an improvement of more than a factor of 10 over previous theoretical studies. Applying the same method to At, the electron affinity of At is predicted to be 2.3729…
Theoretical approaches to the photoionization of few-electron atoms are discussed. These include nonequilibrium Greens functions and wave function based approaches. In particular, the Multiconfiguration Time-Dependent Hartree-Fock method is discussed and applied to a model one-dimensional atom with four electrons. We compute ground state energies and the time-dependent photoionization by the field a strong laser pulse with two different frequencies in the ultraviolet.
Modern challenges arising in the fields of theoretical and experimental physics require new powerful tools for high-precision electronic structure modelling; one of the most perspective tools is the relativistic Fock space coupled cluster method (FS-RCC). Here we present a new extensible implementation of the FS-RCC method designed for modern parallel computers. The underlying theoretical model, algorithms and data structures are discussed. The performance and scaling features of the implementation are analyzed. The software developed allows to achieve a completely new level of accuracy for pr…
Multiconfiguration Dirac-Fock and Relativistic Configuration Interaction methods have been employed to predict the structure and the width of $Kα_{1,2}$ x-ray lines of Al and Si. The influences of electron correlation and inclusion of possible satellite contributions on spectra structure have been studied. The widths of $K$ and $L_{2,3}$ atomic levels of Al and Si have been also computed.
Multiconfiguration Hartree-Fock (MCHF) and multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations are performed for the $2p^{5}~^{2}P^{o}$, $2p^4(^{3}P)3s~^{4}P$, $2p^4(^{3}P)3s~^{2}P$ and $2p^4(^{3}P)3p~^{4}S^o$ states of $^{19}$F~I to determine their hyperfine constants. Several computing strategies are considered to investigate electron correlation and relativistic effects. High-order correlation contributions are included in MCHF calculations based on single and double multireference (SD-MR) expansions. The largest components of the single reference MCHF wave functions are selected to …
Describing time-dependent many-body systems where correlation effects play an important role remains a major theoretical challenge. In this paper we develop a time-dependent many-body theory that is based on the two-particle reduced density matrix (2-RDM). We develop a closed equation of motion for the 2-RDM employing a novel reconstruction functional for the three-particle reduced density matrix (3-RDM) that preserves norm, energy, and spin symmetries during time propagation. We show that approximately enforcing $N$-representability during time evolution is essential for achieving stable solu…
