At finite temperature a nanometer scale Au nanocrystallite can adopt transient atomic configurations by the diffusion of atoms on its surface. Recently the probabilities for various transient sites have been calculated using a Monte Carlo method and a simple classical potential[1,2] The purpose of this study has been to explore the consequences of transient configurations at the ab inito level. A 79 atom unsupported Au nanocrystallite was investigated using periodic DFT with PAW psuedopotentials and the PW91 density functional. The adsorption energy of CO molecules on various sites of the nanocrystallite are calculated. The nanocrystallite is considered in its most probable atomic configuration and in several transient configurations. Kinetic barriers for transformation of the nanocrystallite are also calculated using the nudged elastic band method. We find a trend of increasing CO adsorption energy with decreasing coordination of the Au site[3,4]. We also find that CO adsorbed on transient sites can tend to stabalise the nanocrystallite in a less truncated morphology. These results have important implications for catalysis and deactivation of catalysts.
[1] K. P. McKenna, P. V. Sushko and A. L. Shluger, J. Phys. Chem. C Lett. 111, 2823 (2007)
[2] K. P. McKenna, P. V. Sushko and A. L. Shluger, (Submitted to J. Phys. Chem.)
[3] N. Lopez et al., J. Catal. 223, 232 (2004)
[4] L. M. Molina and B. Hammer, Phys. Rev. B 69, 155424 (2004) |