Multiple solutions in the refinement of ab initio force constants

Abstract

The existence of a double minimum in the refinement of the force constants of the water molecule to ab initio energies is reported. The indeterminacy arises because of an unsatisfactory distribution of points, as defined by their molecular geometries, and may be removed by further calculation of energies at selected geometries. The claim that Diab and Simons' ρ coordinate [3] is superior as an expansion variable for the representation of ab initio energy surfaces has been reassessed.