An efficient parallel coupled cluster program for distributed memory computers

by Janowski, Tomasz; Pulay, Peter

Coupled Cluster methods are often important, e.g., for weak interactions, but for larger systems are practical only on parallel computers. The efficiency of our new parallel CCSD program derives from its formulation in terms of matrix multiplications. Parallelization uses the recently developed Array Files. We can perform CCSD and QCISD energy calcns. of unprecedented size on modest PC clusters, e.g, QCISD/aug-cc-pVQZ (1512 basis functions) on the benzene dimer. This capability enables us to test the additivity of basis set and higher order correlation contributions for π-π interactions. Other benchmark calcns. (naphthalene dimer, nucleic acid base pairs) will also be presented. We have developed less expensive, but still very accurate approxns., such as the use of MP2 amplitudes for weak localized pairs. However, unlike in local correlation techniques, our goal is to closely reproduce full-accuracy results. Current work is focused on adding triple substitutions, and using natural orbitals for distant pairs.