Dimers of Dimers (DOD): A New Fragment-Based Method Applied to Large Water Clusters.

We have developed a dimer-based two-body interaction model, denoted "dimers of dimers" (DOD), for the study of water clusters using a fragmentation approach. By including a second layer at a lower level of theory (e.g., Hartree-Fock), our DOD2 model accurately reproduces the total energies of water clusters ranging in size from 16 to 100 molecules using the MP2 method with a variety of basis sets. The mean absolute error in the calculated DOD2 total energy for a broad range of calculations is only 0.83 kcal/mol. The size of the fragments is independent of the cluster size, and the number of fragments grows fairly slowly with the cluster size. Our results suggest that our method should be applicable for the study of large water clusters.