New AuN (N=27-30) Lowest Energy Clusters Obtained by Means of an Improved DFT-Genetic Algorithm Methodology

The aim of the current study is to explore the structural evolution of neutral and negatively charged gas-phase gold clusters in the size range of 27-30 atoms. We conducted an improved Genetic Algorithm global search combined with the density functional theory study, which we present and explain. New and lower energy structures are reported; these new structures are found to exhibit core shell structures with the number of core atoms increasing with cluster size. Important discrepancies were observed in the energy ranking and energy differences of the obtained geometries when two different functionals (TPSS and PBE) are used. In general terms Au-27(-) and Au-28(-) clusters form nanotube-like structures, whereas that geometry changes into cage-like structures for Au-29(-) and Au-30(-). On the contrary, structures related to a fcc fragment were found to own lower energies for the neutral systems for Au-27, Au-28, and Au-29, while for Au-30 a nonsymmetric cage with one core atom was the lowest-energy isomer. The obtained structures reveal generic structural motifs and structural trends for gold clusters in this size range, which will be valuable for future studies.