Abstract
We introduce a new molecular theory beyond the Born–Oppenheimer approximation, where both electrons and nuclei are treated quantum mechanically and equivalently. First, we develop the coupled mean-field theory (CMFT) for both the electronic and nuclear fields. Then, to take into account the dynamic correlation between these particles, we develop a new molecular theory using the generator coordinate method (GCM) based upon the CMFT, which enables us to calculate the molecular eigenstate and eigenvalue directly. Finally, we apply this method to a water molecule and analyze the isotope effect on the vibrational frequency and the particle density. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 629–637, 1998
