12 research outputs found
Generalized relativistic small-core pseudopotentials accounting for quantum electrodynamic effects: construction and pilot applications
A simple procedure to incorporate one-loop quantum electrodynamic (QED)
corrections into the generalized (Gatchina) nonlocal shape-consistent
relativistic pseudopotential model is described. The pseudopotentials for Lu,
Tl, and Ra replacing only inner core shells (with principal quantum numbers
for the two former elements and for the latter one) are
derived from the solutions of reference atomic SCF problems with the
Dirac-Coulomb-Breit Hamiltonian to which the model Lamb shift operator added.
QED contributions to atomic valence excitation energies evaluated at the SCF
level are demonstrated to exceed the errors introduced by the pseudopotential
approximation itself by an order of magnitude. Pilot applications of the new
model to calculations of excitation energies of two-valence-electron atomic
systems using the intermediate-Hamiltonian relativistic Fock space coupled
cluster method reformulated here for incomplete main model spaces are reported.
Implications for high-accuracy molecular excited state calculations are
discussed
Optical cycling in charged complexes with Ra-N bonds
The extension of laser cooling and trapping techniques to polyatomic
molecular ions would have advanced scientific applications such as search of
physics outside of the Standard Model, ultracold chemistry etc. We apply the
Fock space relativistic coupled cluster method to study low-lying electronic
states of molecular ions with Ra--N bonds, namely RaNCH, RaNH and
RaNCCH. Prospects of laser cooling of these species are estimated, and
the peculiarities of unpaired-electron distributions are analyzed from the
point of view of the molecular electronic structure. RaNH and
RaNCCH are the first symmetric top molecular ions expected to be suitable
for direct laser cooling
Finite-Field Calculations of Transition Properties by the Fock Space Relativistic Coupled Cluster Method: Transitions between Different Fock Space Sectors
Reliable information on transition matrix elements of various property operators between molecular electronic states is of crucial importance for predicting spectroscopic, electric, magnetic and radiative properties of molecules. The finite-field technique is a simple and rather accurate tool for evaluating transition matrix elements of first-order properties in the frames of the Fock space relativistic coupled cluster approach. We formulate and discuss the extension of this technique to the case of transitions between the electronic states associated with different sectors of the Fock space. Pilot applications to the evaluation of transition dipole moments between the closed-shell-like states (vacuum sector) and those dominated by single excitations of the Fermi vacuum (the 1h1p sector) in heavy atoms (Xe and Hg) and simple molecules of heavy element compounds (I2 and TlF) are reported
Relativistic Fock-space Coupled Cluster Method:Theory and Recent Applications
Four-component relativistic all-order multireference electron correlation approaches are the most accurate methods available for benchmark calculations of properties of heavy atoms and their compounds with complex (frequently quasi-degenerate) electronic shell structures. Benchmarking requires continued improvement of the relativistic Hamiltonian aiming at a fully covariant description, as well as the development of high-level correlation methods suitable for general open shell systems. One of the best relativistic many-body approaches available for the purpose is the multi-root, multi-reference Fock space coupled cluster (FSCC) method. FSCC is size extensive, includes both dynamic and non-dynamic electron correlation effects to infinite order, and usually gives the most precise results within the 4-component no-virtual-pair approximation (NVPA). The relativistic FSCC method and its recent modifications and applications are described. We also briefly discuss perspectives for future developments and applications of relativistic FSCC including the challenges of introducing covariant many-body QED methods suitable for use in Fock space methodology in quantum chemistry and atomic physics
Relativistic Fock-space Coupled Cluster Method:Theory and Recent Applications
Four-component relativistic all-order multireference electron correlation approaches are the most accurate methods available for benchmark calculations of properties of heavy atoms and their compounds with complex (frequently quasi-degenerate) electronic shell structures. Benchmarking requires continued improvement of the relativistic Hamiltonian aiming at a fully covariant description, as well as the development of high-level correlation methods suitable for general open shell systems. One of the best relativistic many-body approaches available for the purpose is the multi-root, multi-reference Fock space coupled cluster (FSCC) method. FSCC is size extensive, includes both dynamic and non-dynamic electron correlation effects to infinite order, and usually gives the most precise results within the 4-component no-virtual-pair approximation (NVPA). The relativistic FSCC method and its recent modifications and applications are described. We also briefly discuss perspectives for future developments and applications of relativistic FSCC including the challenges of introducing covariant many-body QED methods suitable for use in Fock space methodology in quantum chemistry and atomic physics
Adsorption of the astatine species on a gold surface: A relativistic density functional theory study
LIBGRPP: A Library for the Evaluation of Molecular Integrals of the Generalized Relativistic Pseudopotential Operator over Gaussian Functions
Generalized relativistic pseudopotentials (GRPP) of atomic cores implying the use of different potentials for atomic electronic shells with different principal quantum numbers give rise to accurate and reliable relativistic electronic structure models of atoms, molecules, clusters, and solids. These models readily incorporate the effects of Breit electron–electron interactions and one-loop quantum electrodynamics effects. Here, we report the computational procedure for evaluating one-electron integrals of GRPP over contracted Gaussian functions. This procedure was implemented in a library of routines named LIBGRPP, which can be integrated into existing quantum chemistry software, thus enabling the application of various methods to solve the many-electron problem with GRPPs. Pilot applications to electronic transitions in the ThO and UO2 molecules using the new library and intermediate-Hamiltonian Fock space relativistic coupled cluster method are presented. Deviations of excitation energies obtained within the GRPP approach from their all-electron Dirac–Coulomb–Gaunt counterparts do not exceed 50 cm−1 for the 31 lowest-energy states of ThO and 110 cm−1 for the 79 states of UO2. The results clearly demonstrate that rather economical tiny-core GRPP models can exceed in accuracy relativistic all-electron models defined by Dirac–Coulomb and Dirac–Coulomb–Gaunt Hamiltonians
Ab initio study of electronic states and radiative properties of the AcF molecule
Relativistic coupled-cluster calculations of the ionization potential,
dissociation energy, and excited electronic states under 35,000 cm are
presented for the actinium monofluoride (AcF) molecule. The ionization
potential is calculated to be IP cm, and the ground state is
confirmed to be a closed-shell singlet and thus strongly sensitive to the
,-violating nuclear Schiff moment of the Ac nucleus.
Radiative properties and transition dipole moments from the ground state are
identified for several excited states, achieving an uncertainty of 450
cm for the excitation energies. For higher-lying states that are not
directly accessible from the ground state, possible two-step excitation
pathways are proposed. The calculated branching ratios and Franck-Condon
factors are used to investigate the suitability of AcF for direct laser
cooling. The lifetime of the metastable state, which can be
used in experimental searches of the electric dipole moment of the electron, is
estimated to be of order 1 ms