THIRD-ORDER MANY-BODY PERTURBATION THEORY FOR INTERMOLECULAR INTERACTIONS .1. HARTREE-FOCK LEVEL

摘要

A zero-order wave function of a dimer is defined as the antisymmetrized product of monomer Hartree-Fock wave functions. A symmetry-adapted many-body perturbation theory is developed up to the third order to obtain interaction energies at the Hartree-Fock level. Correlation effects are accounted for at the second order. The theory is based on second quantization to ensure full symmetry forcing. Intermolecular overlap effects are handled by the biorthogonal formulation. Test calculations on dimers of He, H-2, HF, and water show that the third-order results are very accurate. No ''instability'' due to the use of biorthogonal orbitals was observed. (C) 1997 John Wiley & Sons, Inc. [References: 28]