Global Potential Energy Surfaces with Correct Permutation Symmetry by Multiconfiguration Molecular Mechanics

In the framework of the previously developed multiconfiguration molecular mechanics (MCMM) method, we present a new algorithm for constructing global potential energy surfaces that are invariant with respect to the exchange of identical nuclei. We illustrate the new algorithm by its application to the HOH' ' + H' → OH + H'H' ', OH' + HH' ', OH' ' + HH', HOH' + H' ', and H' 'OH' + H reactions. As part of the MCMM methodology, the new scheme can be used to generate multidimensional global PESs for both small and large systems where a few reaction pathways need to be treated as symmetrically equivalent.