Cusped gaussian wave functions

An orbital-fitting procedure has been used to fit the s- and p-orbitals expressed in terms of a cusped gaussian basis onto Clementi's accurate SCF orbitals. The results suggest that approximately double-zeta accuracy may be obtained for the s-orbitals with a basis of two 1s gaussians per orbital supplemented by a single 1s cusp function for the representation of the orbitals at and near the nucleus, and for the p-orbitals with a basis of three 2p gaussians per orbital plus the 2p cusp function. It is proposed that for the s-orbitals the cusped gaussian basis is superior to both the all-gaussian and Slater function bases for the purpose of molecular calculations. The results are less conclusive for the p-orbitals and, although the efficiency of the basis increases with increasing nuclear charge, further investigation is necessary before a definite conclusion may be reached as to the usefulness of the cusped gaussian basis for the representation of p-orbitals.