Surfaces and Clusters of Mg(NH₂)₂ Studied by Density Functional Theory Calculations

Abstract

Mg(NH 2 ) 2 was studied by bulk, slab, and cluster calculations based on density functional theory within the generalized gradient approximation. Mg(NH 2 ) 2 is confirmed to have a tetragonal unit cell belonging to the space group I4 1 /acd. Five different slabs and their corresponding cleavage energies have been calculated. The most stable surface was the (112) surface, supported by low cleavage energy, special symmetry properties, and small structural changes found during ionic relaxation. Comparison of the density of states calculated from bulk, slab, and clusters indicated that occupied states in the band gap of clusters can be one reason why complex hydrides with nanoparticle structure have enhanced kinetics (in addition to the increased surface area). Calculations of the energy change during removal of NH 3 and H 2 showed that it is energetically easier to remove NH 3 than H 2 from Mg(NH 2 ) 2 , confirming a general trend for metal-N-H systems.

Li–Mg–N–H-based combination systems for hydrogen storage

“…2 shows the crystal structure of Mg(NH 2 ) 2 determined by the neutron diffraction. It can be seen that the Mg 2+ cation is tetrahedrally coordinated by four amide [NH 2 ] − anions [57,58]. The typical IR absorption peaks of N-H vibration modes and H-N-H deformation vibration modes of Mg(NH 2 ) 2 are centered at 3325, 3274 and 1572 cm −1 , respectively [55].…”