THE INFLUENCE OF THE O-H STRETCH AND O-CENTER-DOT-CENTER-DOT-CENTER-DOT-O DISTANCE ON THE MANY-BODY INTERACTIONS IN THE CYCLIC WATER TRIMER

The effects of the O-H stretch and changes in the O ... O distance upo n the one-, two- and three-body interaction energy components were stu died in a cyclic water trimer. Calculations were carried out using sup ermolecular Moller-Plesset perturbation (S-MPPT) theory in conjunction with perturbation theory of intermolecular forces, also known as inte rmolecular Moller-Plesset theory (I-MPPT). The dependence of the one-b ody relaxation as well as electrostatic, induction, exchange and dispe rsion terms upon changes in the intramolecular O-H bond length and upo n the intermolecular O ... O distance were studied to identify the ter ms which have the strongest influence on the structural parameters of the trimer. We found that the one- body terms must be evaluated at a h igh level of theory (MP4) with an elaborate basis set. The two-body pe rturbation energies appear to be reliably reproduced through the secon d order (MP2), and the three-body terms are reliable already at the se lf consistent field (SCF) level of theory. The two-body and three-body terms vary approximately linearly with the OH stretch of proton-donor s.