Parallelization of multi-reference coupled-cluster method

A parallel computer program performing orthogonally spin-adapted two-refere nce state-universal coupled-cluster calculations with singly and doubly exc ited clusters (SUCCSD) is described. It is demonstrated that a significant speedup of the SUCCSD calculations on shared-memory parallel systems having 16-32 CPUs can be achieved with relatively few changes in a serial code, i f the OpenMP directives are used. The parallel efficiency of the SUCCSD cal culations improves with the basis set. The results of parallel SUCCSD calcu lations for the low lying electronic states of simple quasi-degenerate mole cular systems are reported. (C) 2000 Elsevier Science B.V. All rights reser ved.