Reduced hamiltonian orbitals. II. Optimal orbital basis sets for the many-electron problem

Optimal orbital exponents are approximated by minimization of the reduced Hamiltonian orbital ground state energy. They appear to be as good as and are obtained at much less expense than the values derived by the usual SCF exponent optimization scheme. Partitioning of energy into 0-energy, 1-energy, and 2-energy (Absar and Coleman, Int. J. Quant. Chem. 10 , 319 (1976); Chem. Phys. Lett. 39 , 60 (1976)) is used to study the variation in the electronic energy surface upon variation of orbital exponents. The 1-energy operator, the natural orbitals of which are the reduced Hamiltonian orbitals, is compared with the SCF operator.