Two-step method for precise calculation of core properties in molecules
A.V.Titov, N.S.Mosyagin, A.N.Petrov, and T.A.Isaev
Petersburg Nuclear Physics Institute RAS
Gatchina, St.-Petersburg 188300, RUSSIA
Precise calculations of ``core'' properties which are described by the
operators heavily concentrated in atomic cores, like to hyperfine structure
(HFS) and P,T-parity nonconservation (PNC) effects, usually require
accounting for relativistic effects. Unfortunately, even completely
relativistic calculations of diatomics containing elements from fourth period
are very consuming already on the stages of calculation and transformation of
two-electron integrals with a basis of four-component spinors. The
complexity of such calculations becomes very high for compounds of d- and,
especially, f-elements.
In turn, the relativistic effective core potential (RECP) calculations of
``valence'' (spectroscopic, chemical etc.) properties of molecules are very
popular now because the RECP method allows one to treat satisfactory the
correlation and relativistic effects in the valence region of a molecule with
minimal efforts. However, the accuracy of the conventional RECPs is
limited [1]. Besides, the valence molecular spinors are usually smoothed in
atomic cores and, as a result, direct calculation of electronic densities
near heavy nuclei is impossible.
The former circumstance stimulated further development of the RECP approaches
and, in particular, the generalized RECP (GRECP) concept was proposed [1]
employing the idea of different treatment of inner core, outer core and
valence shells. The latter had led to the methods of nonvariational [2] and
variational [3] one-center restoration of correct shapes of four-component
spinors in atomic cores after a two-component (G)RECP calculation of a
molecule. In the report, the restoration and correlation methods are
discussed and their efficiency is illustrated in calculations of HFS and PNC
effects in heavy-atom molecules [2].
The present work was supported by U.S. CRDF grant No. RP2-2339-GA-02 and RFBR
grant No. 03-03-32335. N.M. is supported by the grants of the Leningrad
district governor and Russian science support foundation. A.P. is
grateful to the Ministry of Education RF (Grant PD02-1.3-236) and to
St.Petersburg Committee on Science and HE (Grant PD03-1.3-60). T.I. thanks
INTAS for Grant YSF 2001/2-164.
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A.N.Petrov et al., Phys.Rev.Lett. 88, 073001 (2002);
T.A.Isaev et al., Phys.Rev.A (Rapid Comm.), in press.
[3] A.V.Titov, Int.J.Quant.Chem. 57, 453 (1996).