First-principles study on thermodynamical stability of metal borohydrides: Aluminum borohydride Al(BH4)3

Abstract

The thermodynamical stability of $\mathrm{Al}(\mathrm{B}{\mathrm{H}}_4{)}_3$ has been investigated using first-principles calculations based on density functional theory. The heats of formation are obtained to be -132 and $-131kJ/mol$ without the zero-point energy corrections for $\alpha$- and $\beta$-$\mathrm{Al}(\mathrm{B}{\mathrm{H}}_4{)}_3$, respectively, which are made up of discrete molecular $\mathrm{Al}(\mathrm{B}{\mathrm{H}}_4{)}_3$ units. It is predicted correctly that the $\alpha$ phase is more stable than the $\beta$ phase. The energy difference between the solid phases and the isolated molecule is only about 10 kJ/mol. An analysis of the electronic structure also suggests the weak interaction between $\mathrm{Al}(\mathrm{B}{\mathrm{H}}_4{)}_3$ molecules in the solid phases. It is confirmed that $\mathrm{Al}(\mathrm{B}{\mathrm{H}}_4{)}_3$ obeys the linear relationship between the heat of formation and the Pauling electronegativity of the cation, which has been proposed in our previous study [Nakamori {\it et al.}, Phys. Rev. B {\bf 74}, 045126 (2006)].

5 pages, 5 figures, Proceedings of MH2006 (Maui, October 1-6, 2006)