Noninteger principal quantum numbers increase the efficiency of Slater-type basis sets: double-zeta approximation

Roothaan-Hartree-Fock calculations are performed for the 53 atoms, He throu gh Xe, using a double-zeta (DZ) basis set of extended Slater-type functions whose principal quantum numbers are allowed to be variationally optimum no ninteger values. The resultant wave functions are considerably more accurat e than those obtained from the conventional DZ method which implicitly rest ricts the quantum numbers to be integer values: The largest improvement is found for the Cu atom, where the total energy error 0.214 hartrees of the c onventional DZ method, relative to the Hartree-Fock-limit value, is reduced to 0.043 hartrees by the present method. The noninteger principal quantum numbers also improve the orbital energies. (C) 2000 Elsevier Science B.V. A ll rights reserved.