COMPARATIVE-STUDY OF ERRORS IN HEH- INTERACTION ENERGY CALCULATIONS

Basis set truncation error (BSTE), size extensivity Error (SEE), zero point vibrational energy (ZPVE), and basis set superposition error (BS SE) of HeH- weak van der Waals interaction energy were determined and compared at the self-consistent field (SCF), many-body perturbation th eory (MBPT), and coupled cluster (CC) methods using even-tempered func tions. Isotope substitution effects and the role of bond function augm entation were taken into account. Apart from core correlation energy e rror (CCEE), which is absent from HeH- interaction energy, the results confirm that BSTE is the most important source of error, followed by SEE of the truncated configuration interaction (CI) expansion, ZPVE an d BSSE in a descending order. introducing quadrable excitations to the truncated CI expansion reduces the magnitude of SEE by similar to 45. 7%, and BSSE correction is not necessary even at the electron correlat ion level. While bond function augmentation reduces BSSE at the Hartre e-Fock, it has an oscillating behavior at the electron correlation lev el. (C) 1998 John Wiley & Sons, Inc.