Relativistic basis set selection of heavy atom and the application of direct methods to the RSCF calculation

Abstract

Application of relativistic SCF(RSCF) calculations using basis set expansions on the systems containing heavy element is important, but difficult. Two areas of particular difficulties are investigated and improvements are suggested. One is basis set selection and the other is the SCF procedure. RSCF calculation is very time consuming so that the exponent optimization technique like nonrelativistic case is not practical. Various difficulties in many aspects caused by the extremly large basis set size due to small components are discussed. Extended basis sets of I, Br, and At atom are generated through a rational strategy. The quality of these basis sets are partially examined for the numerical stability. The application of new SCF algorithm, called Direct SCF, on RSCF calculation is useful in several aspects. The four-component RSCF calculation even on medium sized system, requires handling a large integral set. Large integral set is also one of the serious problems in the conventional methods which can be handled by Direct SCF method. And the small magnitudes of density matrices of small component is additional profit in calculation by the Direct RSCF method. General strategy is discussed and the over all procedures are outlined.