Regular Article

First-principles study of molecular hydrogen adsorption on Mg_n Zr (n = 1 ~ 11) clusters^⋆

College of Materials Science and Engineering, Sichuan University, Sichuan Chengdu 610065, P.R. China

^a e-mail: shengyong69@163.com

Received: 27 September 2018
Received in final form: 24 December 2018
Published online: 7 May 2019

Abstract

The geometrical structure, stability, hydriding properties of Mg_nZr (n=1 ~ 11) clusters are studied by the B3LYP method of the density functional theory (DFT) at 6-31+G* (for Mg, H atoms) and Lanl2dz (for Zr atom) levels. The results show that, in most cases, the basic framework of the host Mg_nZr clusters can’t be changed by the adsorption of H₂ and the H₂ molecule prefers a dissociative chemisorption. The Zr atoms tend to stay in the center of clusters and the stability of Mg_nZr clusters becomes better after hydrogenation by comparing the electronic properties, such as VIP and VEA parameters, HOMO-LUMO gaps and chemical hardness. The Mg₃ZrH₂, Mg₆Zr and Mg₈ZrH₂ have better distribution uniformity and symmetry of spin density, indicating better structural stability. Calculated chemisorption energy of the Mg₃ZrH₂ cluster is found maximum in the series. The NEC and DOS of Mg₃ZrH₂ further illuminate the charge transfer and orbitals interactions among the atoms of Mg₃ZrH₂, which suggests the chemical stability after the adsorption of H₂. Finally, the calculated enthalpy difference further confirms the chemisorption of hydrogen on Mg_nZr clusters and the clusters Mg_nZrH₂ (for n=3, 6 and 8) are more exothermic than other considered clusters.