Relativistic SCF calculations for atoms and molecules

Abstract

In the relativistic SCF calculations using basis set expansions for the molecules and atomic spinors, the basis set must satisfy the special relation between the large and the small component of spinor. The large size of the basis set required in the relativistic SCF calculations becomes one of the major sources of computational difficulties. A method of obtaining basis set of practical size which variationally safe is devised and tested for highly positive uranium ions. The present method is based upon the fitting of numerical atomic spinors obtained by numerical Dirac-Fock calculations, using Slater type functions. The quality of basis set obtained by this method has been investigated for various types of large and small component basis sets in an effort to find the optimum strategy. The properties of the relativistic virtual orbitals are investigated by testing whether the Koopman``s theorem is a reasonable approximation for ionization potentials in the relativistic SCF calculations as in the nonrelativistic case. In order to demonstrate the reproduction of the nonrelativistic limit in the relativistic SCF calculations for nonhydride diatoms, relativistic calculations for CO molecule are performed, and the results are quite encouraging.