The thermodynamical stability of ${ \rm Al(BH_4)_3}$ has been investigated using first-principles calculations based on density functional theory. The heats of formation are obtained to be -132 and $-131 { \rm kJ/mol}$ without the zero-point energy corrections for $\alpha$- and $\beta$-${ \rm Al(BH_4)_3}$, respectively, which are made up of discrete molecular ${ \rm Al(BH_4)_3}$ 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 ${ \rm Al(BH_4)_3}$ molecules in the solid phases. It is confirmed that ${ \rm Al(BH_4)_3}$ 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)].
Categories: cond-mat.mtrl-sci