High-pressure structural phase transitions and electronic properties of the alkali hydride compounds XH (X=K, Rb and Cs)

The equilibrium structural parameters, structural phase transition as well the electronic properties of XH compounds have been computed by using the first-principles calculations based on density-functional theory (DFT) and the full-potential linearized augmented plane-wave (FP-LAPW) method. The generalized gradient approximation (GGA) has been used for the exchange-correlation potential. The equilibrium structural parameters such as the lattice constant, the bulk modulus and the pressure-induced phase transition were calculated for rocksalt (RS), cesium chloride (CsCl), zincblende (ZB) and wurtzite (WZ) structures. The GGA, modified Becke-Johnson (mBJ-GGA) and Yukawa screened hybrid functional (YS-PBE0) schemes have been used to calculate the electronic properties. The mBJ-GGA and YS-PBE0 schemes have been found to be more accurate than GGA in computing the energy-band gap. An agreement of our results with the experimental and results of the other theoretical work indicate its reliability. The compounds under our investigation are found to be wide band gap semiconductors within the GGA, and insulators using the mBJ-GGA and YS-PBE0 approaches.