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 Super-Heavy Elements (SHE) from the
"island of stability" (with nuclear charges Z=108 to 118), some of which
were recently synthesized by Oganessian's group , 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 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 . 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  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  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.
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