AB-INITIO HARTREE-FOCK CALCULATIONS OF THE INTERACTION ENERGY OF BIOMOLECULAR COMPLEXES

A systematic study of basis set superposition error (BSSE)-free Hartre e-Fock interaction energies for bimolecular complexes has been carried out. The BSSE corrections were performed using Mayer's chemical Hamil tonian approach with conventional energy (CHA/CE) and compared with th e Boys-Bernardi counterpoise correction scheme. A total of 46 differen t basis sets were used, ranging from minimal to large polarized (13s8p 2d1f/8s2p1d)/[8s5p2d1f/5s2p1d] basis sets, on a total of eight systems containing hydrogen and first-row atoms only. The convergence of the BSSE-free interaction energy is studied as a function of basis set siz e. Corrected interaction energies are generally converged once polariz ation functions are added. Systems could be classified into two types depending on the presence or absence of multiple bonds. The limiting b ehavior of the interaction energy and the BSSE content as N --> infini ty for Pople's STO-NG, N-21G and N-31G basis sets, was predicted by Wy nn's epsilon method. A full study of p, d, and f polarization function s was carried out using the fixed (13s8p/8s)/[8s5p/5s] basis as a star ting point.