Multiphase density functional theory parameterization of the interatomic potential for silver and gold

Abstract

The ground state energies of Ag and Au in the face-centered cubic (FCC), body-centered cubic (BCC), simple cubic (SC) and the hypothetical diamond-like phase, and dimer were calculated as a function of bond length using density functional theory (DFT). These energies were then used to parameterize the many-body Gupta potential for Ag and Au. We propose a new parameterization scheme that adopts coordination dependence of the parameters using the well-known Tersoff potential as its starting point. This parameterization, over several phases of Ag and Au, was performed to guarantee transferability of the potentials and to make them appropriate for studies of related nanostructures. Depending on the structure, the energetics of the surface atoms play a crucial role in determining the details of the nanostructure. The accuracy of the parameters was tested by performing a 2 ns MD simulation of a cluster of 55 Ag atoms – a well studied cluster of Ag, the most stable structure being the icosahedral one. Within this time scale, the initial FCC lattice was found to transform to the icosahedral structure at room temperature. The new set of parameters for Ag was then used in a temperature dependent atom-by-atom deposition of Ag nanoclusters of up to 1000 atoms. We find a deposition temperature of 500 ± 50 K where low energy clusters are generated, suggesting an optimal annealing temperature of 500 K for Ag cluster synthesis. Surface energies were also calculated via a 3 ns MD simulation.