Three-body effects in hydrogen fluoride: survey of potential energy surfaces

The potential energy surface for trimers of hydrogen fluoride is examined for multiple arrangements of the three-molecule cluster. Several established approaches to model the potential energy are examined, including a strictly pairwise additive potential, an established polarizable potential model, another, strictly three-body polarizable model, and a three-body potential recently fitted to accurate ab initio calculations. These potential surfaces are compared to MP2/6-311++G** and SCF/6-311++G** ab initio calculations performed here for each configuration. In each case the overall trimer potential is examined, as well as the three-body contribution to it (obtained by subtracting the sum of the interactions taken pairwise). The effective pair potential has some correspondence to the ab initio calculations, although it generally displays a shallower minimum energy. The established polarizable model has a more repulsive core that compensates for a deeper attractive well that it has adopted to better describe phase-coexistence data. In contrast, the new three-body polarizable model shows better correspondence with the ab initio potential-energy surface.