A highly efficient algorithm for electron repulsion integrals over relativistic four-component gaussian-type spinors

摘要

In the previous studies, a highly efficient computational scheme has been proposed for the Dirac-Hartree-Fock and the Dirac-Kohn-Sham solutions using the generally contracted kinetically balanced Gaussian-type spinors (GTSs).Nevertheless, the calculations based on the full Dirac Hamiltonian are limited to small systems if they contain heavy elements. The bottleneck is the calculation of the two-electron repulsions over the four-component GTSs. The present paper presents an improved algorithm for evaluation of the four-component relativistic integrals. The new algorithm fully exploits the transfer relation of Head-Gordon and Pople (HGP) and the accompanying coordinate expansion (ACE) formulas of ishida. The HGP transfer relation can reduce the four-component integral into several common two-center integrals (pO|qO),which can be computed rapidly using the ACE method. The algorithm is implemented into the four-component program system REL4D. Benchmark calculations demonstrate that a good performance is achieved, particularly for the calculation of the (SS|SS) integrals.