arXiv subjects

N. S. Mosyagin

Publications and source records attributed to N. S. Mosyagin.

33 records · Page 2Linked to original sources

arXiv2005

In search of the electron electric dipole moment: relativistic correlation calculations of the P,T-violation effect in the ground state of HI$^+$

We report the first results of ab initio relativistic correlation calculation of the effective electric field on the electron, E_eff, in the ground state of the HI$^+$ cation. This value is required for interpretation of the suggested experiment on search for the electron electric dipole moment. The generalized relativistic effective core potential, Fock-space relativistic coupled cluster with single and double cluster amplitudes and spin-orbit direct configuration interaction methods are used, followed by nonvariational one-center restoration of the four-component wavefunction in the iodine core. The calculated value of E_eff by the coupled cluster method is E_eff=0.345\times 10^{24}Hz/e*cm. Configuration interaction study gives E_eff=0.336\times 10^{24}Hz/e*cm (our final value). The structure of chemical bonding and contributions to E_eff in HI$^+$ is clarified and significant deviation of our value from that obtained in Ravaine etal Phys.Rev.Lett., 94, 013001 (2005) is explained.

physics.atom-ph↗

arXiv2005

Configuration interaction calculation of hyperfine and P,T-odd constants on ^{207}PbO excited states for the electron EDM experiments

We report first configuration interaction calculations of hyperfine constants A_\parallel and the effective electric field W_d acting on the electric dipole moment of the electron, in two excited electronic states of ^{207}PbO. The obtained hyperfine constants, A_\parallel = -3826 MHz for the a(1) state and A_\parallel = 4887 MHz for the B(1) state, are in very good agreement with the experimental data, -4113 MHz and 5000 \pm 200 MHz, respectively. We find W_d = -(6.1 ^{+1.8}_{-0.6}) 10^{24} Hz/(e cm) for a(1), and W_d = (8.0 \pm 1.6) 10^{24} Hz/(e cm) for B(1). The obtained values are analyzed and compared to recent relativistic coupled cluster results and a semiempirical estimate of W_d for the a(1) state.

physics.atom-ph↗

arXiv2005

Accounting for correlations with core electrons by means of the generalized relativistic effective core potentials: Atoms Hg and Pb and their compounds

A way to account for correlations between the chemically active (valence) and innermore (core) electrons in the framework of the generalized relativistic effective core potential (GRECP) method is suggested. The "correlated" GRECP's (CGRECP's) are generated for the Hg and Pb atoms. Only correlations for the external twelve and four electrons of them, correspondingly, should be treated explicitly in the subsequent calculations with these CGRECP's whereas the innermore electrons are excluded from the calculations. Results of atomic calculations with the correlated and earlier GRECP versions are compared with the corresponding all-electron Dirac-Coulomb values. Calculations with the above GRECP's and CGRECP's are also carried out for the lowest-lying states of the HgH molecule and its cation and for the ground state of the PbO molecule as compared to earlier calculations and experimental data. The accuracy for the vibrational frequencies is increased up to an order of magnitude and the errors for the bond lengths (rotational constants) are decreased in about two times when the correlated GRECP's are applied instead of earlier GRECP versions employing the same innercore-outercore-valence partitioning.

physics.chem-ph↗

arXiv2005

Study of P,T-Parity Violation Effects in Polar Heavy-Atom Molecules

Investigation of P,T-parity nonconservation (PNC) phenomena is of fundamental importance for physics. Experiments to search for PNC effects have been performed on TlF and YbF molecules and are in progress for PbO and PbF molecules. For interpretation of molecular PNC experiments it is necessary to calculate those needed molecular properties which cannot be measured. In particular, electronic densities in heavy-atom cores are required for interpretation of the measured data in terms of the P,T-odd properties of elementary particles or P,T-odd interactions between them. Reliable calculations of the core properties (PNC effect, hyperfine structure etc., which are described by the operators heavily concentrated in atomic cores or on nuclei) usually require accurate accounting for both relativistic and correlation effects in heavy-atom systems. In this paper, some basic aspects of the experimental search for PNC effects in heavy-atom molecules and the computational methods used in their electronic structure calculations are discussed. The latter include the generalized relativistic effective core potential (GRECP) approach and the methods of nonvariational and variational one-center restoration of correct shapes of four-component spinors in atomic cores after a two-component GRECP calculation of a molecule. Their efficiency is illustrated with calculations of parameters of the effective P,T-odd spin-rotational Hamiltonians in the molecules PbF, HgF, YbF, BaF, TlF, and PbO.

physics.atom-ph↗

arXiv2005

Generalized RECPs accounting for Breit effects: uranium, plutonium and superheavy elements 112, 113, 114

The Generalized Relativistic Effective Core Potential (GRECP) method is described which allows one to simulate Breit interaction and finite nuclear models by an economic way and with high accuracy. The corresponding GRECPs for the uranium, plutonium, eka-mercury (E112), eka-thallium (E113) and eka-lead (E114) atoms are generated. The accuracy of these GRECPs and of the RECPs of other groups is estimated in atomic numerical SCF calculations with Coulomb two-electron interactions and point nucleus as compared to the corresponding all-electron Hartree-Fock-Dirac-Breit calculations with the Fermi nuclear charge distribution. Different nuclear models and contributions of the Breit interaction between different shells are studied employing all-electron four-component methods.

physics.chem-ph↗

arXiv2004

Two-step method for precise calculation of core properties in molecules

Precise calculations of core properties in heavy-atom systems which are described by the operators heavily concentrated in atomic cores, like to hyperfine structure and P,T-parity nonconservation effects, usually require accounting for relativistic effects. Unfortunately, completely relativistic treatment of molecules containing heavy elements is very consuming already at the stages of calculation and transformation of two-electron integrals with a basis set of four-component spinors. In turn, the relativistic effective core potential (RECP) calculations of valence (spectroscopic, chemical etc.) properties of molecules are very popular because the RECP method allows one to treat quite satisfactory the correlation and relativistic effects for the valence electrons of a molecule and to reduce significantly the computational efforts. The valence molecular spinors are usually smoothed in atomic cores and, as a result, direct calculation of electronic densities near heavy nuclei is impossible. In the paper, the methods of nonvariational and variational one-center restoration of correct shapes of four-component spinors in atomic cores after a two-component RECP calculation of a molecule are discussed. Their efficiency is illustrated in correlation calculations of hyperfine structure and parity nonconservation effects in heavy-atom molecules YbF, BaF, TlF, and PbO.

physics.atom-ph↗

arXiv2004

In search of the electron dipole moment: Ab initio calculations on ^207PbO excited states

We report ab initio correlated relativistic calculations of the effective electric field W_d acting on the electron in two excited electronic states of PbO, required for extracting the electric dipole moment of the electron from an ongoing experiment at Yale, which has the potential of improving accuracy for this elusive property by several orders of magnitude. The generalized relativistic effective core potential and relativistic coupled cluster methods are used, followed by nonvariational one-center restoration of the four-component wavefunction in the heavy atom core. W_d is -3.2\times 10^24 Hz/ecm for the a(1) state and -9.7\times 10^24 Hz/ecm for the B(1) state. Comparison of calculated and experimental values of the hyperfine constant A_{\parallel} provides an accuracy check for the calculation.

physics.atom-ph↗

arXiv2003

Accounting for Breit interaction in actinide and superheavy element compounds: 1. General remarks

The incorporation of the Breit interaction in atomic and molecular calculations is discussed in the framework of four-component all-electron and two-component relativistic effective core potential (RECP)formalisms. Contributions of the Breit interaction between different core and valence shells are studied in the Dirac-Fock approximation for the uranium, plutonium, ekathallium (Z=113), ekalead (Z=114) and other heavy atoms. It is shown that the two-electron Breit effects between the valence electrons can be neglected for "chemical accuracy" (1 kcal/mol) of calculation of spectroscopic properties of systems containing superheavy elements and actinides whereas large core-core and core-valence Breit contributions can be efficiently described by one-electron RECP operators. Different versions of the generalized RECPs with the Breit interaction taken into account are constructed for uranium and plutonium and tested in comparison with the corresponding all-electron four-component calculations.

physics.chem-ph↗

arXiv2003

Accuracy and efficiency of modern methods for electronic structure calculation on heavy- and superheavy-element compounds

The methods which are actively used for electronic structure calculations of low-lying states of heavy- and superheavy-element compounds are briefly described. The advantages and disadvantages of calculations with the Dirac-Coulomb-Breit Hamiltonian, Huzinaga-type pseudopotential, shape-consistent Relativistic Effective Core Potential (RECP) and Generalized RECP are discussed. The nonvariational technique of the electronic structure restoration in atomic cores after the RECP calculation of a molecule is presented. The features of some approaches accounting for electron correlation, the configuration interaction and coupled cluster methods, are also described. The results of calculations on E113, E114, U and other heavy-atom systems are presented.

physics.chem-ph↗

arXiv2002

Calculation of $P_ and $T_ odd effects in $"" sup 205_TIF including electron correlation

A method and codes for two-step correlation calculation of heavy-atom molecules have been developed, employing the generalized relativistic effective core potential and relativistic coupled cluster (RCC) methods at the first step, followed by nonvariational one-center restoration of proper four-component spinors in the heavy cores. Electron correlation is included for the first time in an ab initio calculation of the interaction of the permanent P,T-odd proton electric dipole moment with the internal electromagnetic field in a molecule. The calculation is performed for the ground state of TlF at the experimental equilibrium, R_e=2.0844 A, and at R=2.1 A, with spin-orbit and correlation effects included by RCC. Calculated results with single cluster amplitudes only are in good agreement (3% and 1%) with recent Dirac-Hartree-Fock (DHF) values of the magnetic parameter M; the larger differences occurring between present and DHF volume parameter (X) values, as well as between the two DHF calculations, are explained. Inclusion of electron correlation by GRECP/RCC with single and double excitations has a major effect on the P,T-odd parameters, decreasing M by 17% and X by 22%.

physics.chem-ph↗

arXiv2001

GRECP/5e-MRD-CI calculation of the electronic structure of PbH

The correlation calculation of the electronic structure of PbH is carried out with the Generalized Relativistic Effective Core Potential (GRECP) and MultiReference single- and Double-excitation Configuration Interaction (MRD-CI) methods. The 22-electron GRECP for Pb is used and the outer core 5s, 5p and 5d pseudospinors are frozen using the level-shift technique, so only five external electrons of PbH are correlated. A new configuration selection scheme with respect to the relativistic multireference states is employed in the framework of the MRD-CI method. The [6,4,3,2] correlation spin-orbit basis set is optimized in the coupled cluster calculations on the Pb atom using a recently proposed procedure, in which functions in the spin-orbital basis set are generated from calculations of different ionic states of the Pb atom and those functions are considered optimal which provide the stationary point for some energy functional. Spectroscopic constants for the two lowest-lying electronic states of PbH ($^2Π_{1/2}, ^2Π_{3/2}$) are found to be in good agreement with the experimental data.

physics.chem-ph↗

arXiv2000

GRECP/MRD-CI calculations of the spin-orbit splitting in the ground state of Tl and of the spectroscopic properties of TlH

The generalized relativistic effective core potential (GRECP) approach is employed in the framework of multireference single- and double-excitation configuration interaction (MRD-CI) method to calculate the spin-orbit (SO) splitting in the $^2P^o$ ground state of the Tl atom and spectroscopic constants for the $0^+$ ground state of TlH. The 21-electron GRECP for Tl is used and the outer core 5s and 5p pseudospinors are frozen with the help of the level shift technique. The spin-orbit selection scheme with respect to relativistic multireference states and the corresponding code are developed and applied in the calculations. In this procedure both correlation and spin-orbit interactions are taken into account. A [4,4,4,3,2] basis set is optimized for the Tl atom and employed in the TlH calculations. Very good agreement is found for the equilibrium distance, vibrational frequency, and dissociation energy of the TlH ground state ($R_e=1.870 Å, ω_e=1420 cm^{-1}, D_e=2.049 eV$) as compared with the experimental data ($R_e=1.868 Å, ω_e=1391 cm^{-1}, D_e=2.06 eV$).

physics.chem-ph↗

arXiv2000

Comments on "Effective Core Potentials" [M.Dolg, Modern Methods and Algorithms of Quantum Chemistry (Ed. by J.Grotendorst, John von Neumann Institute for Computing, Jülich, NIC Series, Vol.1, ISBN 3-00-005618-1, pp.479-508, 2000)]

The recent paper of M.Dolg is discussed and his critical remarks with respect to the Generalized Relativistic Effective Core Potential (GRECP) method are shown to be incorrect. Some main features of GRECP are discussed as compared with the ``energy-consistent/adjusted'' pseudopotential and with the conventional shape-consistent RECP.

physics.chem-ph↗

arXiv2000

Generalized Relativistic Effective Core Potential Method: Theory and calculations

In calculations of heavy-atom molecules with the shape-consistent Relativistic Effective Core Potential (RECP), only valence and some outer-core shells are treated explicitly, the shapes of spinors are smoothed in the atomic core regions and the small components of four-component spinors are excluded from calculations. Therefore, the computational efforts can be dramatically reduced. However, in the framework of the standard nodeless radially local RECP versions, any attempt to extend the space of explicitly treated electrons more than some limit does not improve the accuracy of the calculations. The errors caused by these (nodeless) RECPs can range up to 2000 $cm^{-1}$ and more for the dissociation and transition energies even for lowest-lying excitations that can be unsatisfactory for many applications. Moreover, the direct calculation of such properties as electronic densities near heavy nuclei, hyperfine structure, and matrix elements of other operators singular on heavy nuclei is impossible as a result of the smoothing of the orbitals in the core regions. In the present paper, ways to overcome these disadvantages of the RECP method are discussed. The developments of the RECP method suggested by the authors are studied in many precise calculations of atoms and of the TlH, HgH molecules. The technique of nonvariational restoration of electronic structure in cores of heavy atoms in molecules is applied to calculation of the P,T-odd spin-rotational Hamiltonian parameters including the weak interaction terms which break the symmetry over the space inversion (P) and time-reversal invariance (T) in the PbF, HgF, BaF, and YbF molecules.

physics.chem-ph↗

arXiv1998

Electric dipole moment of the electron in YbF molecule

Ab initio calculation of the hyperfine, P-odd, and P,T-odd constants for the YbF molecule was performed with the help of the recently developed technique, which allows to take into account correlations and polarization in the outercore region. The ground state electronic wave function of the YbF 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 ytterbium in the framework of a non-variational procedure. Core polarization effects are included with the help of the atomic Many Body Perturbation Theory for Yb atom. For the isotropic hyperfine constant A, accuracy of our calculation is about 3% as compared to the experimental datum. The dipole constant Ad (which is much smaller in magnitude), though better than in all previous calculations, is still underestimated by almost 23%. Being corrected within a semiempirical approach for a perturbation of 4f-shell in the core of Yb due to the bond making, this error is reduced to 8%. Our value for the effective electric field on the unpaired electron is 4.9 a.u.=2.5E+10 V/cm.

physics.atom-ph↗