NONINTEGER PRINCIPAL QUANTUM NUMBERS INCREASE THE EFFICIENCY OF SLATER-TYPE BASIS-SETS

Roothaan-Hartree-Fock (RHF) calculations are carried out for the groun d states of the atoms from helium to xenon using a minimal basis set o f Slater-type functions whose principal quantum numbers are allowed to take variationally optimal noninteger values. The resulting energies are substantially superior to those obtained previously under the usua l restriction that principal quantum numbers be positive integers. The energy lowering relative to the single-zeta wave functions of Clement i and co-workers ranges from 0.0066 E(h) in He to 11.2 E(h) in Xe. Our results are superior to those obtained by Hojer using a minimal basis set of unconventional binomially screened basis functions. Noninteger principal quantum numbers benefit d-orbitals the most; physically rea listic negative d-orbital energies are obtained in all cases including those transition-metal atoms for which a conventional single-zeta STF basis leads to positive d-orbital energies. (C) 1997 John Wiley & Son s, Inc.