High-level Ab InitioEvidence of Bipyramidal Cu5Clusters as FluxionalJahn-Teller Molecules.

Abstract

Novel highly selective synthesis techniques have enable the production of atomically precise monodisperse metal clusters (AMCs) of subnanometer size. These AMCs exhibit `molecule-like' structures that have distinct physical and chemical properties, significantly different from those of nanoparticles and bulk material. In this work, we study copper pentamer Cu5clusters as model AMCs by applying both density functional theory (DFT) and high-level (wave-function-based) ab initiomethods, including those which are capable of accounting for the multi-state multi-reference character of the wavefunction at the conical intersection between different electronic states and augmenting the electronic basis set till convergence. After assessing the accuracy of a high-level multi-multireference ab initioprotocol for the well-known Cu3case, we apply it to demonstrate that bypiramidal Cu5clusters are distorted Jahn-Teller (JT) molecules. The method is further used to evaluate the accuracy of single-reference approaches, finding that the coupled cluster singles and doubles and perturbative triples CCSD(T) method are very closeto our ab initiopredictions.Finally, we discuss how JT effects and, more generally, conical intersections, are intimately connected to the fluxionality of AMCs, giving them a `floppy' character that ultimately facilitates their interaction with environmental molecules and thus enhances their functioning as catalysts.