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.