Two-parameter exponential-type basis functions for atomic calculations

It is found that ordinary STO s fall off too fast in the atomic region in many cases. A new type of basis set, which is more adaptable to the rather different requirements of the various atomic orbitals in an atom, is developed. The suggested functional form χ(r) = Nr^n-1 exp{?α(βr + 1)^1/2 ? 1]} contains the STO s as a limiting case. Calculations on a series of atoms from H to Zn show that the new basis gives better results than STO s for equal basis set size. The necessary integrals do not present any problem to evaluate.