SIXTH-ORDER MANY-BODY PERTURBATION THEORY .2. IMPLEMENTATION AND APPLICATION

摘要

Based on a cluster operator formulation of sixth-order Moller-Plesset (MP6) perturbation theory equations for the calculation of MP6 in terms of spin-orbital two-electron integrals are derived. Efficiency has been gained by systematically using intermediate arrays for the determination of energy contributions resulting from disconnected cluster operators. In this way, the maximum cost factor of O(M(12)) (M being number of basis functions) is reduced to O(M(9)). The implementation of MP6 on a computer is described. The reliability of calculated MP6 correlation energies has been checked in three different ways, namely (a) by comparison with full configuration interaction (CI) results, (b) by using alternative computational routines that do not involve intermediate arrays, and (c) by taking advantage of relationships between fifth-order and sixth-order energy contributions. First applications of the MP6 method are presented. (C) 1996 John Wiley & Sons, Inc. [References: 18]