The convergence properties of hindered rotor energy levels

The Schrِdinger equation describing one-dimensional hindered rotation of one CHO group against the other in glyoxal is solved variationally using three sets of basis functions and an experimentall derived potential taken from the literature. Reference states are defined by the free rotor potential, a single well potential and a double well potential. Of the basis sets studied, the double well reference states provide the most rapidly convergent reference functions for solving the full hindered rotor Hamiltonian. In the case of the free rotor and double well reference states, unusual patterns to convergence were observed for the cis levels.