Ab initio calculations of the optical properties of alanates

We present a study of the electronic structures of the complex hydrides LiAlH4, NaAlH4, Mg(AlH4)2, Li3AlH6, and Na3AlH6 using density functional theory calculations. Quasi particle corrections are calculated in the GW approximation. We show that where in the simple hydrides it is mainly the dispersion that determines the shape of the dielectric function in the complex hydrides it is the energy level splitting that is dominant. Furthermore we show that the positions of the energy levels in the complex hydrides is strongly dominated by the aluminum hydrogen clusters and their mutual interactions. The positive alkali (earth) ions do only contribute details to the electronic structure that do not influence the dielectric functions significantly