Decoupled Hartree‐Fock methods. II. Calculation of the potential curves of diatomic molecules

Applying an extended form of the Mulliken approximation and a monopole approximation for the Coulomb integrals the Hartree‐Fock nonorthogonal energy expression is decoupled. Thus, the total energy splits into a sum of one‐electron increments. The increments are minimized directly with respect to the linear coefficients and orbital exponents. Further, the ZDO approximation is used in the decoupled energy expression to avoid difficulties arising in connection with the evaluation of multicenter integrals. “Rigid core” calculations were carried out for the valence electrons of first‐row diatomics. In case of nonpolar molecules good results are obtained for equilibrium distances and force constants. The method fails for molecules with atoms having very different nuclear charges.