Water-benzene interactions: an effective fragment potential and correlated quantum chemistry study.

Structures and binding in small water-benzene complexes (1-8 water molecules and 1-2 benzene molecules) are studied using the general effective fragment potential (EFP) method. The lowest energy conformers of the clusters were found using a Monte Carlo technique. The binding energies in the smallest clusters (dimers, trimers, and tetramers) were also evaluated with second order perturbation theory (MP2) and coupled cluster theory (CCSD(T)). The EFP method accurately predicts structures and binding energies in the water-benzene complexes. Benzene is polarizable and consequently participates in hydrogen bond networking of water. Since the water-benzene interactions are only slightly weaker than water-water interactions, structures with different numbers of water-water, benzene-water, and benzene-benzene bonds often have very similar binding energies. This is a challenge for computational methods.