Effect of temperature on the structure of Pd8 and Pd7Au1 clusters: an Ab initio molecular dynamics approach

Density functional theory (DFT) is currently one of the most utilized theoretical approaches to analyze physical and chemical properties of metal clusters, which are of interest in economically important applications such as catalysis. In this respect, the important role of temperature has been scarcely considered mainly because this variable is not part of the DFT model and other theoretical ab initio schemes. In this work, we present an ab initio molecular dynamics study of Pd8 and Pd7Au1 clusters to understand, to a degree, the effect of doping on the structural stability of palladium clusters as a function of temperature. A combined strategy using both empirical potential and DFT calculations is employed to obtain lowest-energy configurations for Pd8 and Pd7Au1 clusters, which are later subject to Born–Oppenheimer molecular dynamics simulations at finite temperatures. The structural stability as a function of temperature is evaluated through an analysis of the total energy dispersion with respect to the average energy of clusters at different thermodynamic states. Results show that the effect of doping Pd cluster with one Au atom gives rise to a decreasing of the structural stability. In the range of temperatures studied, atomic diffusion is not observed for Pd8 cluster, while Pd7Au1 cluster shows Pd-Au dimer diffusion at 300 K toward different faces of the 6-atom Pd octahedron structural motif. Preliminary data suggest that melting transition is about 250 K for this bimetallic cluster.