Accurate three-dimensional potential energy surface for H/sub 3/

An accurate three-dimensional potential energy surface for H/sub 3/ has been obtained by the configuration interaction (CI) method. The calculated energies, for 156 nuclear configurations, with the energy of the saddle point taken to be zero, are believed to lie within 0.1 kcal/mole of the exact clamped-nuclei limit. The CI calculations used an extended one-particle basis set of 4 s-type, 3 p-type, and 1 d-type contracted Gaussian functions, and a nearly complete n-particle basis set. In order to solve the large secular problem, the direct CI method was adapted to the problem of complete CI for three valence electrons. The properties of the accurate H/sub 3/ potential surface were used to evaluate ab initio and semiempirical methods for potential surface calculations, with emphasis on their applications to other exchange reactions.