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 of the water dimer system in the limit of very extended basis set have been computed. The most extended even tempered basis set (548 functions) included diffuse f gaussian functions on oxygen and d functions on hydrogen. The effect of functions with higher angular momentum has been investigated by a different scheme. The basis set superposition error (BSSE) was avoided in an a priori fashion by applying the SCF-MI method. Bader analysis showed that the amount of charge transferred between the interacting units agrees with that computed by standard SCF supermolecule wave functions. The geometry of the system was optimised using the algorithm implemented into GAMESS-US program based on analytic first derivatives of the SCF-MI energy. The resulting SCF-MI interaction energy was estimated to be -3.45 kcal/mol, in close accordance with 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