Theoretical characterization of non-covalent weakly bound clusters through the application of sophisticated computational quantum chemistry methodologies and the development of integrated fragmentation techniques

Non-covalent, weakly bound clusters have been and remain of significant interest to many researchers. However, with computational studies, accurate description of these interactions requires sophisticated electronic structure methods employing large basis sets. This methodology becomes extremely computationally demanding as the size of the system increases. This work presents benchmark data and explores methods for obtaining highly accurate ab initio results for larger systems at greatly reduced computational costs. CCSD(T) complete basis set limit interaction energies are presented for a variety of parallel-slipped pi...pi dimers and low-lying isomers of (H 2O)6. The calibration of a 2-body:Many-body fragmentation method for computing interaction energies of several (H2O) n clusters with n ranging from 3-10 is performed. As a result, 2-body:Many-body QM:QM approach is extended to a 3-body:Many-body technique. In addition to calculating the energetics, the 2-body:Many-body fragmentation method, which is cast within the ONIOM framework, is used for the determination of Cartesian analytic gradients for the purpose of geometry optimizations.