Thermodynamic functions from lattice dynamic of KMgH3 for hydrogen storage applications

The dynamic and the thermodynamic properties of KMgH3 have been investigated by density functional theory (DFT). We have found that the calculated lattice parameters differ from the experimental data by less than 0.6% and the electronic density of states (DOS) reveals that the KMgH3 is an insulator. The formation energy of KMgH3 from binary hydrides (MgH2 and KH) has been calculated. Using density-functional perturbation theory, we have calculated the phonon dispersion curves, the phonon density of states, the Born effective charge tensors, the dielectric permittivity tensors and the phonon frequencies at the center of the Brillouin zone of KMgH3. Also we have assigned the calculated phonon frequencies at the gamma point for Infrared-active and Raman-active modes. For the first time, the thermodynamic functions are computed using the phonon density of states.

► The dynamical and thermodynamic properties of KMgH3 are presented. ► The density of state is calculated and shows that the KMgH3 is an insulator. ► Formation energy of the KMgH3 is calculated for different possible reaction pathways. ► The phonon frequencies at gamma point for the infrared and Raman modes are assigned. ► The thermodynamic functions of KMgH3 are determined for the first time in this study.