Grid-based numerical Hartree-Fock solutions of polyatomic molecules

Numerical solutions of the Hartree-Fock (HF) equation of polyatomic molecules have been obtained by an extension of the numerical density-functional method of Becke and Dickson [J. Chem. Phys. 89, 2993 (1988); 92, 3610 (1990)]. A finite-difference method has been used to solve Poisson's equation for the Coulomb and exchange potentials and to evaluate the action of the Laplace operator on numerical orbitals expanded on an interlocking multicenter quadrature grid. Basis-set-limit HF results for an atom and diatomic and triatomic molecules are presented with the total energies and the highest occupied orbital energies converged to within 10(-5) Hartree without any extrapolation.