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

Abstract

The geometrical structure, stability, hydriding properties of MgnZr (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 MgnZr 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 MgnZr 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 MgnZr clusters and the clusters MgnZrH2 (for n=3, 6 and 8) are more exothermic than other considered clusters.