Improvement of polarized double-zeta basis sets for molecular interactions. Complexes of NH3, OH2, and FH with H+ and Li+

Interaction energies of a proton and lithium cation with NH₃, OH₂, and HF axe computed at the SCF and Møller-Plesset levels. It is found that the basis set superposition errors at all levels with the 6-3 1G** basis set may be greatly reduced by including an additional diffuse sp shell on first-row atoms; the exponent of this shell has been optimized to 0.1.