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1

Large scale multi-configuration Hartree-Fock calculation of the hyperfine structure of the ground state of vanadium

100%

Scharf O., Gaigalas G.

Open Physics

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2006

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vol. 4

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issue 1

42-57

EN

The hyperfine structure of the ground state of vanadium, 51VI, is calculated in the nonrelativistic framework of the multi-configuration Hartree-Fock approximation. A configuration state function limiting algorithm is used to make the calculations feasible and to study the influence of core, valence and core-valence correlations in detail. The obtained configuration state function space captures the most important orbital correlations within 2%. Further correlations are included through configuration interaction calculation. The atomic state functions are used to evaluate the magnetic dipole hyperfine factor A and the electric quadrupole factor B. It turns out that the ab initio calculation can not capture the core polarization of the 2s shell. It introduces an error that is higher than the Hartree-Fock approximation. However, the detailed correlations being observed suggest the introduction of a wrong correlation orbital due to the algorithm being used. Neglecting this orbital leads to good agreement with 2% deviation from the experimental values for the A factors.

2

Hyperfine structure operator in the tensorial form of second quantization

81%

Gaigalas G., Rudzikas Z., Scharf O.

Open Physics

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2004

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vol. 2

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issue 4

720-736

EN

The general tensorial form of the hyperfine interaction operator in the formalism of second quantization is presented. Both diagonal and off-diagnonal matrix elements of the above-mentioned operator are found using an approach based on a combination of second quantization in the coupled tensorial form, angular momentum theory in three spaces (orbital, spin and quasispin) and a generalised graphical technique. This methodology allows us to account for correlation effects efficiently and, therefore, to study the hyperfine interactions in complex many-electron atoms, those with openf-shells included, in a practical manner. All this will lead us to design an efficient program for large scale calculations of hyperfine structure and isotope shift.

3

Theoretical investigation of the electronic structure of a ferroelectric SbSI cluster at a phase transition

61%

Audzijonis A., Gaigalas G., Žigas L., Pauliukas A., Žaltauskas R., Čerškus A., Narusis J.

Open Physics

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2005

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vol. 3

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issue 3

382-394

EN

This paper presents the theoretical investigation of energy levels of valence bands (VB) and core levels (CL) of the ferroelectric SbSl single crystals in antiferroelectric and ferroelectric phases. Since the best approximation for the deep VB levels is a calculation by the Hartree-Fock method, the molecular model of a SbSI crystal was used for calculations. This model of the crystal was also used for calculations of the total density of states. It was found that the VB and CL of this ferroelectric semiconductor are sensitive to the small lattice distortion at the phase transition, and that an average of the total density of states, when all atoms participate in oscillations of all normal modes, are more similar to the experimental X-ray photoelectron spectra (XPS). The experimental splitting of CL obtained by XPS was compared with the theoretically calculated one by two different methods. The cluster model calculations showed that the splitting of the CL in SbSI might be caused by photoelectron emission from the atoms, which have different valence state, at the surface.

4

Investigation of the electronic structure of the SbSeBr cluster

52%

Audzijonis A., Gaigalas G., Žigas L., Pauliukas A., Šalkus B., Žaltauskas R., Kvedaravičius A., Čerškus A., Narušis J.

Open Physics

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2008

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vol. 6

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issue 3

415-421

EN

The energy levels of valence bands (VB) in SbSeBr crystals were calculated for investigation of the photoelectron emission spectra of A5B6C7 - type crystals. The molecular model of this crystal was used for calculation of VB by the Density Functional Theory (DFT) and Unrestricted Hartree - Fock (UHF) methods. The molecular cluster consisting of 20 molecules of SbSeBr was used for calculations of averaged total density of states including atom vibrations. The spectra of averaged total density of states from VB in the SbSeBr cluster were compared with experimental photoelectron emission spectra from VB of A5B6C7 - type crystals. The results of comparison clarify that the atomic vibrations are one of possible reasons for the smoother appearance of the experimental X-ray photoelectron spectrum (XPS).

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Large scale multi-configuration Hartree-Fock calculation of the hyperfine structure of the ground state of vanadium

Hyperfine structure operator in the tensorial form of second quantization

Theoretical investigation of the electronic structure of a ferroelectric SbSI cluster at a phase transition

Investigation of the electronic structure of the SbSeBr cluster