**Generalized Relativistic Effective Core Potentials
for superheavy elements.**

**N.S.Mosyagin, A.V.Titov, A.N.Petrov, T.A.Isaev**

Petersburg Nuclear Physics Institute

**Investigation of physical and chemical properties of relatively long-living**
**isotopes of SuperHeavy Elements (SHE) from an "island of stability"
(with**
**nuclear charges Z=108 to 118), some of which were recently synthesized**
**by Oganessian's group [1], and their compounds is a fundamental
scientific**
**problem. The SHE properties are very difficult for the experimental
study**
**because of their extremely small quantities, only single atoms are
available**
**for research now. Therefore, precise calculations on SHE compounds
are**
**necessary to gain a better understanding of their physics and chemistry,**
**which, as is already known, are essentially different from those
of their**
**lighter homologues by the valence structure [2,3]. The relativistic**
**pseudopotential or Relativistic Effective Core Potential (RECP)
method is**
**one of the most optimal approaches for calculations on molecules**
**containing heavy atoms [4]. In a series of papers [5,6], we have**
**introduced and developed the Generalized RECP (GRECP) technique.**
**This method is described in detail in papers [6] and it allows one
to attain**
**practically any desired (high) accuracy, while requiring moderate**
**computational efforts. It is known that the Breit interaction can
contribute**
**a few hundreds wave numbers even to transition energies between**
**low-lying states of very heavy elements. Undoubtedly, this contribution**
**should be taken into account at precise calculations of such systems.
For a**
**series of SHE, we constructed GRECPs [3] which effectively incorporate**
**the Breit effects. In order to estimate the accuracy of these GRECPs,**
**calculations of transition energies for these atoms were carried
out.**
**Significant improvement of the accuracy in reproducing the all-electron**
**Dirac-Hartree-Fock-Breit results for the GRECP as compared to the**
**tested RECPs of other groups was demonstrated in these calculations.**
**The same number of electrons is explicitly treated in the considered
RECP**
**versions.**
**A.T. and N.M. were supported in part by Scientific Program of**
**St.Petersburg Scientific Center of RAS. T.I. is grateful to INTAS
grant**
**YSF 2001/2-164 for financial support. A.P. is grateful to Ministry
of**
**education of Russian Federation (grant PD02-1.3-236) and to**
**St-Petersburg Committee of science (grant PD02-1.3-236). This work**
**was supported in part by RFBR grant 03-03-32335.**

[1]Yu.Ts.Oganessian, et al., Nature 400, 242 (1999); Yu.Ts.Oganessian,
et al.,

Nature 413, 122 (2001); K.Powell, Nature 418,
815 (2002);

Ch.E.Dullmann, et al., Nature 418, 859 (2002).

[2] U.Kaldor and E.Eliav,

Adv.Quant.Chem. 31, 313 (1999).

[3] A.V.Titov, N.S.Mosyagin, T.A.Isaev, A.N.Petrov,

Accuracy and efficiency of modern methods
for electronic structure

calculation on heavy- and superheavy-element
compounds,

Eprint http://xxx.lanl.gov/abs/physics/0209035;
accepted for

publication in russian journal "Nuclear Physics".

[4] W.C.Ermler, R.B.Ross, P.A.Christiansen,

Adv.Quant.Chem. 19, 139 (1988).

[5] I.I.Tupitsyn, N.S.Mosyagin, A.V.Titov, J.Chem.Phys. 103, 6548 (1995);

N.S.Mosyagin, A.V.Titov, Z.Latajka, Int.J.Quant.Chem.
63, 1107 (1997).

[6] A.V.Titov, N.S.Mosyagin, Int.J.Quant.Chem. 71, 359 (1999);

A.V.Titov and N.S.Mosyagin, Rus.J.Phys.Chem.
[Zh.Fiz.Khimii] 74

(Suppl. 2), S376 (2000).