First-principles study of structural properties of Li$_2$NH

Nitrogen containing hydrides have attracted much attention recently as viable candidates for hydrogen storage materials. One example is the amide and imide involved in the reversible chemical reaction $$ {\rm LiNH}_{2} + {\rm LiH} \rightarrow {\rm Li}_{2}{\rm NH} +{\rm H}_{2}. \label{re1} $$ In an effort to understand the reaction mechanism, one needs to have the informations on the structural properties of these compounds. There is a disagreement in the existing literature regarding the crystal symmetry of Li$_2$NH. We present a summary of first-principles investigations of the structural properties of Li$_2$NH in an attempt to identify the lowest energy structure. Calculations were performed within density functional theory framework employing plane waves and projector-augmented-wave potentials. Various crystal structures were obtained by minimazing the total energy and the forces. The stability and energetics of these structures will be discussed.