Diagrammatic many-body perturbation expansion for atoms and molecules: VII experiments in vector and parallel processing for fourth-order energy terms involving triply excited intermediate states

Abstract

The efficient evaluation of the fourth-order energy terms corresponding to linked diagrams involving triply excited intermediate states which arise in the many-body perturbation expansion for the electron correlation energy of closed-shell atoms and molecules on vector processing and parallel processing computers is discussed. The linked-diagram theorem decouples the many-electron problem allowing efficient implementation on parallel processing machines. Furthermore, the computation associated with each of the resulting subproblems is very well suited to vector processing machines. A “dynamic load balancing” technique is employed in both a dedicated and a multi-user environment. Timing tests are reported for the CRAY X-MP/416 computer. Execution rates in excess of 828 Mflops are observed.