Eur. Phys. J. D (2012) 66: 80
https://doi.org/10.1140/epjd/e2012-20464-3

Regular Article

Theoretical investigation on the structure and electronic properties of bimetallic gold-zinc cluster cations and their monocarbonyls^*

¹ Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, P.R. China
² International Centre for Materials Physics, Academia Sinica, Shenyang 110016, P.R. China

^a e-mail: scumaj@126.com

Received: 9 August 2011
Received in final form: 23 December 2011
Published online: 29 March 2012

Abstract

Using the first principles calculations, the mixed Au_nZn $\begin{array}{}\mathrm{+}\\ \mathit{m}\end{array}$ (n + m ≤ 6) cluster cations and their monocarbonyls Au_nZn_mCO⁺ have been investigated at the PW91 level. For the small Au_nZn $\begin{array}{}\mathrm{+}\\ \mathit{m}\end{array}$, most ground-state isomers are planar structures. A significant odd-even oscillation of the highest occupied-lowest unoccupied molecular orbital energy gaps with the number of Au atoms is observed. Upon CO adsorption, the top site and C head-on adsorptions are most favorable in energy. Moreover, the optimized geometries indicate that the CO molecule prefers binding to Au atom of the Au_nZn $\begin{array}{}\mathrm{+}\\ \mathit{m}\end{array}$ clusters, which can be understood by the frontier molecular orbital theory in detail. From the theoretical calculations, the CO charge population, CO binding energy (BE) and the Gibbs free-energy change ΔG generally decrease with the increase of the Zn content. It is found that the BE is highly related to the electron transfer between CO and the cluster cations. Furthermore, a linear correlation between ΔG and the CO BE is found. The red shift in the CO stretching frequency is sensitive to the cluster size and composition. Our calculation suggests that CO reactive collision on Au₃Zn⁺ and Au₂Zn $\begin{array}{}\mathrm{+}\\ \mathrm{2}\end{array}$ may lead to the dissociation of the clusters with a Zn atom loss.