Electronic Structure and Energetics of the Quaternary Hydride \textbf{Li}$_{4}$\textbf{BN}$_{3}$\textbf{H}$_{10}$

Li$_{4}$BN$_{3}$H$_{10}$ has been synthesized recently from LiNH$_{2}$/LiBH$_{4}$ mixtures and its crystal structure determined. We have calculated the electronic structure of this complex hydride and investigated its thermodynamic stability and decomposition energetics. We find that its enthalpy of formation is --708 kJ/mole with respect to the elemental constituents and --6 kJ/mole relative to a 3:1 molar LiNH$_{2}$/LiBH$_{4}$ mixture, in qualitative agreement with experiment. Reaction enthalpies computed for several decomposition pathways suggest \begin{center} Li$_{4}$BN$_{3}$H$_{10} \quad \to $ Li$_{3}$BN$_{2}+\textstyle{1 \over 2}$Li$_{2}$NH + $\textstyle{1 \over 2}$NH$_{3}$ + 4H$_{2}$ \end{center} as the likely dehydriding route.