HARTREE-FOCK LIMIT PROPERTIES OF THE WATER DIMER IN ABSENCE OF BSSE

A series of calculations has been accomplished employing uncontracted even tempered basis set expansions of increasing dimension, The SCF-MI (self-consistent field for molecular interactions) binding energy and force constant for the O-H stretching involved in the hydrogen bond o f the water dimer system in the limit of very extended basis set have been computed. The most extended even tempered basis set (548 function s) included diffuse f gaussian functions on oxygen and d functions on hydrogen. The effect of functions with higher angular momentum has bee n investigated by a different scheme. The basis set superposition erro r (BSSE) was avoided in an a priori fashion by applying the SCF-MI met hod, Bader analysis showed that the amount of charge transferred betwe en the interacting units agrees with that computed by standard SCF sup ermolecule wave functions. The geometry of the system was optimised us ing the algorithm implemented into GAMESS-US program based on analytic first derivatives of the SCF-MI energy. The resulting SCF-MI interact ion energy was estimated to be - 3.45 kcal/mol, in close accordance wi th recently reported values, The calculated Hartree-Fock limit for the water monomer was - 76.0676 au to be compared with the previous value of - 76.0675 au. (C) 1998 Elsevier Science B.V. All rights reserved.