Ground State Electronic Wave Function of Methane

Abstract

An approximate electronic wave function for the ground state of CH₄, in the equilibrium nuclear configuration, has been obtained by a variational calculation. Approximate Hartree‐Fock molecular orbitals are expanded as linear combinations of a set of basis orbitals of the form f(x, y, z) exp(—ar²) centered on carbon and hydrogen. Five independent s orbitals and two p orbitals on carbon are combined with one simple Gaussian orbital on each hydrogen nucleus. The parameters specifying these orbitals were obtained by preliminary variational calculations on the carbon atom. Correlation effects due to all possible Slater determinants constructed from these orbitals are calculated by a perturbation method. Parallel calculations with the same orbitals were carried out on the ³P ground state of carbon. Calculated ionization potential and dissociation energy are compared with experimental values.