A comparative study between all-electron scalar relativistic calculation and all-electron calculation on the adsorption of hydrogen molecule onto small gold clusters

A comparative study between all-electron relativistic (AER) calculation and all-electron (AE) calculation on the H-2 molecule adsorption onto small gold clusters has been performed. Compared with the corresponding Au (n) H-2 cluster obtained by AE method, the Au (n) H-2 cluster obtained by AER method has much shorter Au-H bond-length, much longer H-H distance, larger binding energy and adsorption energy, higher vertical ionization potentials (VIP), greater charge transfer, higher vibrational frequency of Au-H mode and lower vibrational frequency of H-H mode. The delocalization of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) for Au (n) H-2 cluster obtained by AER method is obvious. All these characteristics suggest that the scalar relativistic effect might strengthen the Au-H bond and weaken the H-H bond. It is believed that the scalar relativistic effect is favourable to the H-2 molecule adsorption onto small gold cluster and the reactivity enhancement of H-2 molecule. It may be one of the reasons why the dissociative adsorptions take place in some Au (n) H-2 clusters. With increasing size of Au (n) H-2 clusters, the influence of scalar relativistic effect becomes more significant. Some further studies focused on the influence of scalar relativistic effect on the adsorption behaviour of other small molecules onto gold clusters are necessary in the future.