LAUSR

Abstract The global optimization of metallic clusters is an important topic because nanoclusters exhibit structure-dependent properties. In this paper, we present a global optimization study of Ag 20 , Au 20 , Ag 55 and Au 55 in their neutral and charge states (−1, 0, +1) conducted using a Parallel-Tempering Molecular Dynamics algorithm at the DFTB level without pre-screening. For Au 20 , Ag 20 and their ions, the present DFTB low energy structures are in good agreement with previously published calculations and experimental data. In the case of Ag 55 - and Au 55 - , the present study is consistent with photo-electron detachment experiments suggesting highly symmetric icosahedral structures for silver and more disordered morphologies for gold. The present results are also compatible with trapped ion electron diffraction experiments and calculations for Ag 55 + and Ag 55 - . We report low-energy isomers of Au 55 exhibiting cavities below their external shell. This work quantitatively confirms the relevance of DFTB for structure calculation of noble metal clusters. Furthermore, it also demonstrates the feasibility of global optimization using DFTB, without pre-screening through classical potential, for sizes up to a few tens of atoms and for different charge states.