Investigation of structural and electronic properties of the MgI2 compound under high pressure by density functional theory

The structural and electronic properties of the MgI₂ compound under high pressure were calculated using density functional theory (DFT) with the SIESTA package program. Under ambient conditions, the MgI₂ compound crystallizes in a trigonal-type structure with space group P3 ̅m1 (Space Group No: 164). This structure contains 3 atoms in its unit cell, and the lattice parameters were calculated as a = b = 4.1308 Å and c = 6.4956 Å. Starting from this structure at 0 GPa, pressure was applied up to 240 GPa in increments of 10 GPa. At 150 GPa, a phase transition occurred to an orthorhombic-type structure with space group Immm (Space Group No: 71). This new structure contains 6 atoms in its unit cell, and the lattice parameters were determined as a = 2.8530 Å, b = 3.1693 Å, and c = 9.5187 Å. To determine which of the two structures is more stable, energy-volume calculations were performed. The results showed that the P3 ̅m1 phase is more stable at lower pressures, whereas the Immm phase becomes more stable at higher pressures. Furthermore, enthalpy calculations were carried out using the obtained energy-volume data, and the phase transition pressure from the P3 ̅m1 phase to the Immm phase was found to be 86.2 GPa. In addition, the electronic properties of the obtained structures were also investigated. While the P3 ̅m1 phase exhibits semiconducting behavior with a direct band gap, the Immm phase shows metallic characteristics. Key Words: DFT, Total Energy, Enthalpy, Phase Transition, Electronic Properties