INVESTIGATING OPTIMAL COORDINATES FOR DESCRIBING VIBRATIONAL MOTION

Results of independent mode models of molecular vibrations of SO2 and H2O are compared to converged eigenvalues and eigenfunctions. Energies of self-consistent-held and adiabatic wave functions are calculated a nd compared to the eigenvalues; Brueckner functions and natural medals are compared to the eigenfunctions. These comparisons are made for a class of normal coordinates of varying curvature. Of the coordinates w e considered, an independent mode model based on rectilinear normal co ordinates provides the best description of the energetics yet provides the poorest description of the eigenfunctions. The ramifications of t his finding are discussed for both independent mode models and perturb ative descriptions of molecular vibrations.