ON THE ROLE OF BOND FUNCTIONS IN INTERACTION ENERGY CALCULATIONS - AR-CENTER-DOT-CENTER-DOT-CENTER-DOT-HCL, AR-CENTER-DOT-CENTER-DOT-CENTER-DOT-H2O, (HF)(2)

We analyze the effect of an extended set of bond functions on the SCF and MP2 interaction energies, and their SAPT perturbation components; electrostatic, induction, dispersion, and exchange. The electrostatic, induction, and exchange terms at the SCF level prove to be largely independent. The dispersion energy is substantially improved and the improvement did not depend much on the bond-function location. In contrast, the electrostatic-correlation term is usually seriously distorted and the distortion strongly dependent on the bond-function location. It was also shown that the distortion may be significantly reduced by appropriate shifting of the location. Only then the interaction energies obtained with bond functions may be considered reliable. It is strongly recommended to control the electrostatic-correlation term. We also present samples of accurate results (within 5% error bar) for the Ar-HCl, Ar-H2O, and (HF)(2) complexes. (C) 1995 American Institute of Physics.