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.