The unbiased density functional-based Birmingham Cluster Genetic Algorithm is employed to locate the global minima of all neutral and mono-ionic silver-gold octamer clusters. Structural, energetic and electronic trends are determined across the series, in order to clarify the role of composition and charge on the position of the 2D–3D transition in ultrasmall coinage metal systems. Our calculations indicate a preference for three dimensional structures at high silver concentrations, which varies significantly with charge. The minimum in composition dependent mixing energies is independent of the charge, however, with a preference for the maximally mixed clusters, Ag4Au4ν for all charge states ν. The sensitivity of isomeric preference to ν is found to be greater for electron-rich and electron-deficient clusters, implying a complexity of unambiguous determination of cluster motifs in related experiments. Vertical ionization potentials and detachment energies are calculated to probe electronic behaviour, providing numerical predictions for future spectroscopic studies.
The calculations reported here have been performed on the following HPC facilities: The University of Birmingham BlueBEAR facility (Reference ); the MidPlus Regional Centre of Excellence for Computational Science, Engineering and Mathematics, funded under EPSRC grant EP/K000128/1 (R.L.J.); and via our membership of the UK's HPC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), this work made use of the facilities of HECToR and ARCHER, the UK's national high-performance computing service, which is funded by the Office of Science and Technology through EPSRC's High End Computing Programme.
A. S. and R. S. acknowledge financial support by the DFG (grant SCHA 885/10-2) and the Merck'sche Gesellschaft für Kunst und Wissenschaft e.V. The authors are thankful for the input of Sven Heiles, who provided optimised neutral cluster structures, and for useful discussions throughout this work.
©2016 Walter de Gruyter Berlin/Boston