The prism algorithm for two‐electron integrals

A new approach to the evaluation of two‐electron repulsion integrals over contracted Gaussian basis functions is developed. The new scheme encompasses 20 distinct, but interrelated, paths from simple shell‐quartet parameters to the target integrals, and, for any given integral class, the path requiring the fewest floating‐point operations ( FLOPS ) is that used. Both theoretical ( FLOP counting) and practical (CPU timing) measures indicate that the method represents a substantial improvement over the HGP algorithm.