PNNL

Abstract

We examine the Many-Body Expansion (MBE) for alkaline earth metal clusters, Ben, Mgn, Can (n = 4, 5, 6) at the MP2, CCSD(T), MRPT2, and MRCI levels of theory. The magnitude of each term in the MBE is evaluated for several geometrical configurations. We find that the behavior of the MBE for these clusters depends strongly on the geometrical arrangement, and, to a lesser extent, on the level of theory used. Another factor that affects the MBE is the in situ (ground or excited) electronic state of the individual atoms in the cluster. For most geometries, the three-body term is the largest, followed by a steady decrease in absolute energy for subsequent terms. Though these systems exhibit non-negligible multi-reference effects, there was little qualitative difference in the MBE expansion when employing single vs. multi-reference methods. Useful insights into the connectivity and stability of these clusters have been drawn from the respective potential energy surfaces and Quasi-Atomic orbitals for the various dimers, trimers, and tetramers. Through these analyses we investigate the similarities and differences in the binding energies of different size clusters for these metals.