AN EFFICIENT TREATMENT OF KINEMATIC FACTORS IN PSEUDO-RELATIVISTIC CALCULATIONS OF ELECTRONIC-STRUCTURE

Relativistic two-electron operators obtained by the Douglas-Kroll tran sformation contain p-dependent kinematic prefactors which are,not pres ent in the corresponding Breit-Pauli operators. These factors are usua lly calculated using a resolution of the identity approach, which requ ires integral transformations. In the present article we describe an a lternative approach, based on a local approximation, where the effect of the prefactors can; be absorbed in the atomic contraction coefficie nts. The effect of the local approximation is investigated in detail. The suggested approach is simple to implement in integral codes that a llow the use of a general contraction scheme.