High thermal properties of cubic MgO: DFT study of stability, electronic, phononic, and optical properties using hybrid exchange correlation functional

Abstract

The current study focuses on examining the electronic, vibrational, thermal, and optical properties of the cubic MgO crystal structure in two different space groups: Fm$\overline{3}$m and Pm$\overline{3}$n identified as MgO-1 and MgO-2, respectively. MgO-1 has high symmetry leading to rather isotropic electronic properties, while MgO-2 is comparably less symmetric causing it to have more directional properties compared to MgO-1. However, MgO-1 demonstrates a wider band gap of 4.47(6.12) eV found by using GGA(HSE06) compared to the band gap of MgO-2's set at 2.89(4.68) eV using GGA(HSE06). This difference in band gaps can be attributed to the electrostatic environment surrounding the atoms in MgO-1 being more uniform. The high symmetry leads to degenerate energy levels contributing to a wider band gap of MgO-1. Through negative formation energy, phonon band structure calculations, and molecular dynamics simulations, we confirm that both phases of cubic MgO are energetically, dynamically and thermally stable. The MgO-2 has a higher phonon density of states and thus heat capacity compared to MgO-1. MgO-1 exhibits higher absorption and a higher maximum refractive index compared to MgO-2, suggesting its suitability for applications requiring strong light interaction. These findings suggest that MgO-1 and MgO-2 could be promising materials for applications requiring specific optical properties, such as optical filters, wave-guides, or nonlinear optical devices.