Structural and electronic properties of Aun (n=2-10) clusters and their interactions with single S atoms:: Ab initio molecular dynamics simulations -: art. no. 155427

The structure and electronic properties of Au-n and AunS (n=2-10) clusters has been demonstrated using an ab initio ultralsoft pseudopotential strategy. The geometry optimization of different isomeric structures was performed under the framework of the spin-polarized density functional theory using the generalized gradient approximation for the exchange correlation energy. The comparison of the ground state geometries between Au-n and AunS clusters revealed that while free Au-n clusters favor planar configuration, the AunS clusters adopt three-dimensional structures starting from n=6 onwards. Up to n=5, the AunS clusters show similar structural conformations as Aun+1 clusters by replacing Au atoms with S. The relative stability of Au-n clusters calculated based on binding energies, atom attachment energy, and a second order difference in energy shows oscillations due to the odd-even electron pairing effect, which differs in the presence of the S atom. In contrast to this, the energy gap between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO) shows strong oscillations for both Au-n and AunS clusters reflecting the contribution of the Au atomic orbitals to construct the HOMO and LUMO energy levels. Finally, the higher stability of Au-6 and Au5S clusters in spite of having even and odd number of electrons, respectively, suggests the dominance of geometrical stability over the electronic shell closure effect.