SURPRISING CASES OF DIVERGENT BEHAVIOR IN MOLLER-PLESSET PERTURBATION-THEORY

High-order Moller-Plesset perturbation calculations have been carried out for several small molecules and compared to full configuration int eraction (FCI) results. The convergence of the Moller-Plesset series i s found to depend crucially on the one-electron basis sets. Addition o f diffuse basis functions leads in some cases to divergent behavior of the Moller-Plesset series, even for highly single reference dominated systems as Ne and HF. The results thus questions the usefulness of hi gher-order perturbation calculations as a vehicle for obtaining arbitr ary accuracy of quantum chemical calculations and raises the fundament al theoretical question: When does Moller-Plesset perturbation theory converge for many-electron systems in extended basis sets? 1996 Americ an Institute of Physics.