A Systematic Search for the Geometric Structures, Stabilities and Electronic Properties of Bimetallic CsAu(0,±1)n Clusters

Abstract

The geometric structures, relative stabilities, growth-pattern behaviors, and electronic properties of neutral and charged CsAun(0,±1) clusters have been systematically investigated with the general gradient approximation (GGA) exchange correlation density functional theory (TPSSTPSS) and a relativistic effective core potential, together with a vibrational frequency anslysis. The optimized geometric structures show that the ground-state structures have three-dimensional (3D) structures from n = 4 and that the doped Cs atoms tend to locate at the symmetry and surface position. One gold-atom-capped CsAun−1(0,±1) structure for CsAun(0,±1) clusters with increasing number of Au atoms is the dominant growth pattern. The total energies and the averaged atomic binding energies exhibit a sequence of CsAun− > CsAun > CsAun+ , which indicates that the stability of anionic CsAun− clusters is higher than that of neutral CsAun clusters and that the CsAun clusters is more stable than the cationic CsAun+ clusters. The relative stabilities are examined based on the analysis of the averaged atomic binding energy and the second-order difference energy, and the results indicate that the CsAu3, CsAu6+ and CsAu2− clusters are the most stable clusters. Based on the analysis of the frontier molecular orbitals, we find that the CsAun(0,±1) (n = 1 − 10) clusters can more easily acquire electrons and that the loss of electrons is difficult. The highest occupied-lowest unoccupied molecular orbital (HOMO-LUMO) gaps exhibit significant even-odd oscillation behavior. The higher gaps are exhibited by neutral CsAun clusters with odd numbers of gold atoms and ionic CsAun±1 clusters with even numbers of gold atoms. Especially, the CsAu3, CsAu6+ and CsAu6− clusters have the highest HOMO-LUMO gaps, which proves again that CsAu3, CsAu6+ and CsAu2− clusters are the most stable and the magic structures. Because of the electronegativity of Au is higher than that of the Cs atom, the charge transfers from the Cs atoms to the Aun frames in the CsAun+1 clusters. Furthermore, we have calculated the dissociation energies and found that the CsAun+ clusters have lower dissociation energies. This indicates that CsAun+ clusters are easy to dissociate and less stable. The dissociation energies of the CsAun and the CsAun− clusters exhibit a generally opposite odd-even behavior.