AN EFFICIENT METHOD OF IMPLEMENTING THE HORIZONTAL RECURRENCE RELATION IN THE EVALUATION OF ELECTRON REPULSION INTEGRALS USING CARTESIAN GAUSSIAN FUNCTIONS

The tree search problem is considered for optimizing the horizontal recurrence relation step, which is a three-dimensional recurrence relation used in generating two-electron integrals. By eliminating redundant work, it is possible to achieve 13%, 25%, 38% and 44% savings in floating point operations and 21%, 34%, 46% and 53% reductions in memory requirements for the (ff\ff), (gg\gg), (hh\hh) and (ii\ii) cases, respectively. These savings and reductions will lead to quite efficient two-electron integral and derivative programs when high angular momentum functions are included.