A quantum chemical study of the utility of property-optimized Gaussian expansions

A modification of a Slater type orbital to includes a logarithmic term which is described. Because of the singularity in the Hamiltonian at r = 0, an eigenfunction of the Hamiltonian also has the singularity at r = 0. A logarithmic term was used in the Slater-type orbital for this purpose. The energies of the first excited state of the hydrogen atom, and of the ground state and the first excited state of the helium atom were calculated. Only the singlet excited state of the helium atom showed an appreciable improvement. The expectation values of one and two electron operators were calculated. Property optimized Gaussian expansions of Slater type orbitals were used to calculate the ground state energy and the one electron molecular properties of the water molecule and the NH2(-) species. The effect of simultaneously using a weighting factor and pseudonormalization was studied.