Neutral and Anionic Gold Decamers: Planar Structure with Unusual Spatial Charge-Spin Separation.

We have investigated the issue of two-dimensional (2D) versus three-dimensional (3D) structures for neutral-state Au10 and clarified the lowest-energy structure among a few 2D Au10(-) isomers. Though almost all previous works were based on density functional theory (DFT), we here carried out not only extensive DFT calculations but also high levels of ab initio calculations of Möller-Plesset second order perturbation theory (MP2), and coupled cluster theory with single and double excitations (CCSD) including perturbative triple excitations [CCSD(T)]. While DFT favors 2D structures, MP2 and CCSD(T) favor 3D structures for moderate-sized basis sets. However, we note that the basis-set superposition error (BSSE) corrections make the ab intio results favor 2D structures too. The near-degeneracy (driven by relativistic effects) of 5d and 6s orbitals of gold helps stabilize acute apex gold atoms, resulting in 2D structures. The planar triangular structures of a local minimum Au10 (triplet) and the global minimum Au10(-) show remarkable spatial charge-spin separation due to their singly occupied molecular orbital(s). By the same reason, Au10(-) shows much larger vertical detachment energy than other even-numbered gold cluster anions.