Density functional studies of structural and electronic properties of potassium alanate as a candidate for hydrogen storage

Potassium Alanate has been one of the goal candidates for hydrogen storage during the past decades. In this report, the Density Functional Theory was initially applied to simulate the electronic and structural characteristics of the experimentally known KAlH4 complex hydride. The relaxation of unit cell parameters and atomic positions was conducted until the total residual force was reduced to less than 0.001eV per unit cell. The final deduced cell parameters of this orthorhombic structure were a=8.834, b=5.763, c=7.328A˚. Calculations were carried out by using the Projected Augmented Plane wave method via the QUANTUM ESPRESSO Package. In the next step, the Density of States calculations together with the band structure results showed that our data coincides with a non-magnetic KAlH4 insulator with a band gap of 5.1eV. In order to investigate the nature of the chemical bonds in the crystal structure, the charge density distribution in (100), (010), (001), and (110) planes, along with the BornEffective charge and Löwdin population was used. The results show the transition of a partial charge from K+ cation to [AlH4]- subunit which leads to an ionic bond.