PARALLEL DIRECT IMPLEMENTATIONS OF 2ND-ORDER PERTURBATION THEORIES

Two algorithms are presented for parallel direct computation of energi es with second-order perturbation theory. Closed-shell MP2 theory as w ell as the open-shell perturbation theories OPT2(2) and ZAPT2 have bee n implemented. The algorithms are designed for distributed memory para llel computers. The first algorithm exhibits an excellent load balance and scales well when relatively few processors are used, but a large communication overhead reduces the efficiency for larger numbers of pr ocessors. The other algorithm employs very little interprocessor commu nication and scales well for large systems. Ln both implementations th e memory requirement has been reduced by allowing the two-electron int egral transformation to be performed in multiple passes and by distrib uting the (partially) transformed integrals between processors. Result s are presented for systems with up to 327 basis functions. (C) 1995 b y John Wiley & Sons, Inc.