The [Au(n),Si](-), n=1-4, potential energy surface: competition between Au-Si and Au-Au bonding

A systematic theoretical investigation of the structure of anionic gold-silicon clusters Au(n)Si(-), n=1-4, has been carried out. The two lowest-lying spin states and all topologically possible connectivities were considered for n=1-3. For n=4, the doublet state and the majority of low-lying geometries were taken into account. Transition states connecting the local minima were identified. Calculation of the density of states of the minima shows that, while Au-Si bonds are enthalpically preferred, the low vibrational frequency of Au-Au bonds makes those entropically favored. The high symmetry of the minimum structures reduces their density of states, up to a factor of 12 for the aurosilane Au(4)Si(-). Under experimental conditions of rapid cooling and inefficient annealing, the Au(2)SiAuAu(-) isomer of C(s) symmetry can be expected to be as abundant as the aurosilane Au(4)Si(-) of T(d) symmetry in the gas phase.