Self-Consistent Molecular-Orbital Methods. VII. Convergence of Gaussian Expansions of Slater-Type Atomic Orbitals in Calculations of First- and Second-Order Properties

Least-squares representations of Slater-type atomic orbitals by a sum of Gaussian-type orbitals are used in self-consistent molecular-orbital calculations of first- and second-order properties. Quadrupole moments and electric field gradients are considered as examples of first-order properties. Diamagnetic susceptibilities, magnetic shielding constants, electrical polarizabilities, and nuclear spin coupling constants are calculated using finite perturbation theory. It is shown that, except for nuclear spin coupling constants, the results converge rapidly (with increasing size of Gaussian expansion) to the values appropriate for pure Slater-type orbitals. A comparison of calculated results with experimental data will be made in a future publication.