Energetic, structure stability, electronic structure, optical properties of Ti0.875Mg0.125H2 crystal from principles calculations

We report a first-principles study of energetic, structural and electronic properties of TiH2 and Ti0.875Mg0.125H2. While the optical properties was studied for only Ti0.875Mg0.125H2. Our calculated structural parameters are found in good agreement with the experiment and other theoretical results. The formation enthalpies are calculated to analyze the stability of the two hydrides. The calculated enthalpy changes show that the stability of Ti0.875Mg0.125H2 is lower than that of TiH2. The electronic density of states reveals that the two hydrides studied here exhibit metallic characteristics. And the origin of the change of density of states for Ti0.875Mg0.125H2 caused by adding magnesium to TiH2 is studied. We also study electronic charge density distribution contours in the (110) crystallographic plane and Mulliken charge populations, which indicates that the bonding nature of the two hydrides is covalent bond between Ti and H and bonds between Ti and H in Ti0.875Mg0.125H2 are weakened by the addition of magnesium. Furthermore, the optical features such as dielectric function, refractive index, extinction coefficient, reflectivity, absorption coefficient, photoconductivity and electron energy-loss function of Ti0.875Mg0.125H2 were calculated for photon energy up to 16 eV. The calculated results show that Ti0.875Mg0.125H2 has a considerable absorption, high photoelectric conversion efficiency for sunlight with the longer wavelengths. These results provide a theoretical basis for preparing Mg-Ti-H photoelectric materials as switchable coatings for solar collector applications.