Two-dimensional, fully numerical solutions of second-order Dirac equations for diatomic molecules. part 3

The exact, four-component second-order Dirac equation in transformed elliptical coordinates is derived for a diatomic system. Numerical solutions are obtained using a point-relaxation approach. The relativistic correction to the total energy of H2+ at R = 2a.u. is found to be −7.365 × 10−6a.u. The deviation from an earlier value of −7.383 × 10−6a.u. by Luke et al. or by Bishop is shown to arise from a spuriously large c−4 term in their Hamiltonian.