Ammonia borane $\left({\text{NH}}_3{\text{BH}}_3\right)$ possesses many appealing properties as a hydrogen storage material; however, the release of trace amounts of borazine during the desorption process is troublesome. Recently, it was found that substitution of one of the H atoms in the ${\text{NH}}_3$ group by Li or Na could significantly improve the hydrogen desorption properties. The resulting lithium amidoborane $\left({\text{LiNH}}_2{\text{BH}}_3\right)$ and sodium amidoborane $\left({\text{NaNH}}_2{\text{BH}}_3\right)$ compounds have been studied by us using density-functional theory. Specifically, we have succeeded in determining the detailed crystal structures of ${\text{LiNH}}_2{\text{BH}}_3$ and ${\text{NaNH}}_2{\text{BH}}_3$, including the atomic positions in their respective unit cells. Calculated hydrogen removal energies of the hydrogen release reactions are found to be in good agreement with the experimental trend.

• Received 2 February 2009

DOI:https://doi.org/10.1103/PhysRevB.79.132102