Onehyphen;Center Perturbation Approach to Molecular Electronic Energies. IV. Tenhyphen;Electron Molecules of Type MHk

摘要

Taking the spherically symmetric molecular puff as the zerohyphen;order problem, we carry out a perturbation calculation of the energies of the HF, H2O, NH3, and CH4molecules. The firsthyphen;order correction function is obtained through the diagonal Sternheimer approximation in which each orbital is perturbed independently by the onehyphen;electron perturbing potential. For the energy increment between puff and molecule, the integral Hellmannndash;Feynman formula is employed. At several Msngbnd;H distances energies are computed, and for H2O and NH3the energy also is examined as a function of the Hsngbnd;Msngbnd;H bond angle. Stretching and bending force constants in H2O, NH3, and CH4are found to have the right order of magnitude, although computed equilibrium internuclear separations are not so good. An extremely flat potential curve near the minimum of the energy gives a poor equilibrium angular geometry in the case of H2O. The inversion barrier of NH3is calculated to be 0.0135 a.u. compared with the experimental value of 0.0093 a.u. It is argued that the integral Hellmannndash;Feynman formula combined with the Sternheimer approximation form a consistent manyhyphen;electron perturbation method.