PARALLEL INTERNALLY CONTRACTED MULTIREFERENCE CONFIGURATION-INTERACTION

A parallel implementation of the internally contracted (IC) multirefer ence configuration (MRCI) module of the MOLPRO quantum chemistry progr am is described. The global array (GA) toolkit has been used in order to map an existing disk-paging small-memory algorithm onto a massively parallel supercomputer, where disk storage is replaced by the combine d memory of all processors. This model has enabled a rather complicate d code to be ported to the parallel environment without the need for t he wholesale redesign of algorithms and data structures. Examples show that the parallel ICMRCI program can deliver results in a fraction of the time needed for equivalent uncontracted MRCI computations. Furthe r examples demonstrate that ICMRCI computations with up to 10(7) varia tional parameters, and equivalent to uncontracted MRCI with 10(9) conf igurations, are feasible. The largest calculation demonstrates a paral lel efficiency of about 80% on 128 nodes of a Gray T3E-300. (C) 1998 J ohn Wiley & Sons, Inc.