Structural formation of binary PtCu clusters: A density functional theory investigation

Abstract

Binary transition-metal clusters have attracted great attention and a large number of studies have been reported, however, our atomistic understanding of the structural formation mechanisms of those clusters is still far from satisfactory. In this paper, we report a systematic study of the PtnCum−n clusters (m=2,3,…,14,n=0,1,…,m) employing Ab-Initio density functional theory calculations within the Perdew–Burke–Ernzerhof functional. Using a set of structural design principles, we obtained a hierarchical set of atomic configurations from which the structural formation mechanisms are discussed in details. We found a negative excess energy for m>2, providing strong evidence favouring the formation of binary PtCu clusters. In general, the Cu atoms tend to form agglomerates located near the center of gravity of the clusters while the Pt atoms tend to lie further away from the center of gravity and separated from each other. Therefore, this behaviour tends to reduce the number of Pt–Pt bonds whereas the number of Cu–Cu and Pt–Cu bonds tends to be maximized. These mechanisms help to release strain energy by means of relaxation of the gas-phase clusters, and the locations of the Cu and Pt atoms suggest that the formation of core–shell like structures starts already in this small size regime. Furthermore, the formation of the PtCu alloy does not lead to changes in the magnetic properties of the clusters in comparison with the parent Pt and Cu clusters. The systematic work presented here provides a basis to understand and tailor the properties of binary cluster.