Investigation of structural, electronic and elastic properties of MgBr2 compound under high pressure by density functional theory

The structural, electronic and elastic properties of 𝑀𝑔𝐵𝑟2 compound under high hydrostatic pressure were examined using the Siesta package program within the framework of density functional theory (DFT). 𝑀𝑔𝐵𝑟2 crystallizes in a trigonal type structure with space group 𝑃3̅𝑚1 under ambient conditions. When gradually increasing pressures of 10 GPa were applied to this structure, phase transformation occurred into a tetragonal type structure with space group 𝐼4/𝑚𝑚𝑚. Total energy and enthalpy calculations were made for these two structures, respectively, in order to obtain the phase transition pressure value that is in better agreement with the experimental results. According to these calculation results, the phase transition pressure was obtained as 101.5 GPa. In addition, the electronic band structure of the 𝑀𝑔𝐵𝑟2 compound was also calculated in order to have more information about its physical properties. Although 𝑀𝑔𝐵𝑟2 has an insulating character with a band gap of 4.4 eV in the 𝑃3̅𝑚1 phase, it has a metallic character since it has no band gap in the 𝐼4/𝑚𝑚𝑚 phase. Finally, elastic constant values were calculated to understand the mechanical and structural stability of the 𝑀𝑔𝐵𝑟2 compound. According to calculations, both 𝑃3̅𝑚1 and 𝐼4/𝑚𝑚𝑚 phases are mechanically and structurally stable. Key Words: Density Functional Theory, Phase Transition, Enthalpy, Structural Properties, Electronic Properties, Elastic Properties