Use of symmetry-adapted Brillouin theorem to analyze the variational content of molecular wave functions along potential energy surfaces: Application to BH2 and PO2

Abstract

The analysis of the Brillouin conditions in a chain of groups is used to explain why self-consistent field (SCF), multiconfigurational SCF (MCSCF), or configuration interaction (CI) methods can lead to an unbalanced description of the potential energy hypersurfaces along symmetry-broken pathways. A Wigner-Racah formulation of the generalized Brillouin theorem is the appropriate theoretical tool for performing such an analysis. We apply this procedure to a Renner-Teller splitting in BH2 and to a pseudo-Jahn-Teller conical intersection in PO2. A systematic ab initio study of both systems leads to the definition of compact CASSCF wave functions which ensure a balanced description of the ground Born-Oppenheimer potential energy surfaces. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 521–541, 1997