Restricted and unrestricted Hartree-Fock calculations on the geometry of the methyl radical

Extensive restricted Hartree-Fock (RHF) calculations are reported for the ground-state potential energy surface for the methyl radical. The surface, formed by computing total energy as a function of pyramidal bending and symmetric stretching of the C-H bonds, clearly reveals that a planar structure corresponds to the minimum energy. Both unrestricted Hartree-Fock (UHF) and RHF calculations using Gaussian-type orbitals give a nonplanar structure; however, calculations utilizing larger basis sets always obtain a geometry which is planar. These results accentuate the problems associated with basis sets that are "inadequate". © 1982 American Chemical Society.