Simultaneous determination of nuclear and electronic wave functions without Born–Oppenheimer approximation: Ab initio NO+MO/HF theory

Abstract

AbstractWe develop a simultaneous determination method of nuclear and electronic wave functions without the Born–Oppenheimer approximation. We examine two expanding methods, namely, molecular orbital (MO)‐type and valence bond (VB)‐type expansions for a nuclear orbital, which is a one‐particle wave function of a nucleus. The VB‐type expansion is shown to be more accurate than the MO‐type one because of the local nature of the nuclei. We also investigate the basis function expansion of the nuclear orbital and propose a scheme to determine the orbital exponent for the nuclear basis function. Numerical calculations confirm the accuracy and feasibility of the present method. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001