Density Functional Studies on Crystal Structure and electronic properties of Potassium Alanate as a candidate for Hydrogen storage

Abstract

Potassium Alanate is one of the goal candidates for hydrogen storage during past decades. In this report, initially the Density Functional Theory was applied to simulate the electronic and structural characteristic of the experimentally known KAlH4 complex hydride. The relaxation of unit cell parameters and atomic positions was performed until the total residual force reduced 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 Projected Augmented Plane wave method via QUANTUM ESPRESSO Package. In the next step, the Density of States calculations together with band structure results, showed that our data coincide with a non-magnetic KAlH4 insulator with a band gap of 5.1ev. In order to investigate the nature of chemical bonds in the crystal structure, the charge density distribution in (100),(010),(001),(110) planes, along with Born Effective charge and Lowdin population was used. The results show the transition of a partial charge from K+ cation to [AlH4]- subunit which leads to an ionic bond.