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N. Mosyagin

Publications and source records attributed to N. Mosyagin.

5 recordsLinked to original sources
arXiv2001

GRECP/RCC calculation of the spectroscopic constants for the HgH molecule and its cation

Generalized relativistic effective core potential (GRECP) calculations of spectroscopic constants of the HgH molecule ground and low excited states and the HgH+ cation ground state are carried out, with correlation included by the Fock-space relativistic coupled cluster (RCC) method. Basis set superposition errors (BSSE) are estimated and discussed. It is demonstrated that connected triple excitations of the 13 outermost electrons are necessary to obtain accurate results for mercury hydride. Spectroscopic constants derived from potential curves which include these terms are in very good agreement with experiment, with errors of a few mbohr in Re, tens of wavenumbers in excitation energies and vibrational frequencies, and proportionately for other properties. Comparison with previous calculations is also presented.

physics.chem-ph↗
arXiv2000

Convergence improvement for coupled cluster calculations

Convergence problems in coupled-cluster iterations are discussed, and a new iteration scheme is proposed. Whereas the Jacobi method inverts only the diagonal part of the large matrix of equation coefficients, we invert a matrix which also includes a relatively small number of off-diagonal coefficients, selected according to the excitation amplitudes undergoing the largest change in the coupled cluster iteration. A test case shows that the new IPM (inversion of partial matrix) method gives much better convergence than the straightforward Jacobi-type scheme or such well-known convergence aids as the reduced linear equations or direct inversion in iterative subspace methods.

physics.chem-ph↗
arXiv1998

All-electron Dirac-Coulomb and RECP calculations of excitation energies for mercury atom with combined CI/MBPT2 method

Calculations of transition energies between low-lying states of mercury atom are performed in the frame of combined CI/MBPT2 method. Results of all-electron relativistic calculations (using the Dirac-Coulomb Hamiltonian) are compared with experimental data and results of other four-component calculations. The results of the RECP calculations are compared with the corresponding all-electron results in order to estimate accuracy of different RECPs. Contributions from correlations in different shells to the calculated excitation energies as well as effects of basis set truncation at different orbital angular momenta, nuclear models, errors in gaussian approximation of the GRECP components are reported. Analysis of the obtained results shows that at least 34 external electrons of mercury atom should be correlated and the one-electron basis set should contain up to h angular momentum functions in order to reach a reliable agreement with experimental data within 200 1/cm. It is concluded that correlations of the 4f electrons can be efficiently taken into account for 20 electron GRECP at the generation stage.

physics.atom-ph↗
arXiv1997

Enhancement of the electric dipole moment of the electron in BaF molecule

We report results of ab initio calculation of the spin-rotational Hamiltonian parameters including P- and P,T-odd terms for the BaF molecule. The ground state wave function of BaF molecule is found with the help of the Relativistic Effective Core Potential method followed by the restoration of molecular four-component spinors in the core region of barium in the framework of a non-variational procedure. Core polarization effects are included with the help of the atomic Many Body Perturbation Theory for Barium atom. For the hyperfine constants the accuracy of this method is about 5-10%.

physics.atom-ph↗