One-Center-Expansion—Configuration-Interaction Studies on CH4 and NH3

One-center-expansion—configuration-interaction calculations have been extended to include higher-order spherical harmonics and extra radial factors. Calculations have also been made to study the prediction of nuclear geometry. Computations on CH4 using as a basis set the orthonormalized Slater atomic orbitals through l=8, yielded a ground-state energy of −39.94 a.u. Further, the inclusion of additional Schmidt orthogonalized radial factors gave much less improvement than the addition of higher spherical harmonics. The calculations with basis orbitals through l=4 on NH3 failed to predict a nonplanar configuration of minimum energy except for the case where the basis set was truncated to include only orbitals through l=2. For the l=2 case NH3 was predicted to have a nonplanar geometry within one degree of the experimental value.