Effect of Defects on the Electronic Structure and Optical Properties of MgO Under High Pressure

Defects and grain boundaries are prevalent in materials and can significantly influence their mechanical, transport, and optical properties, both deep within the Earth and under shock compression. MgO is commonly used as a window material in shock experiments and is a key component of the Earth's lower mantle. Its relatively simple crystal structure makes it a prototype in many condensed matter studies. This study utilizes density functional theory to perform electronic structure and optical property calculations of MgO in the B1 structure under tens-of-GPa pressures. Structures with point defects were generated by adding or removing atom(s) in the unit cell. Grain Boundary structures were generated by considering various cell sizes and misorientation angles. Relaxation calculations were performed for these structures through energy minimization, after which we estimate the defect and grain-boundary formation energies. The electronic structure estimates how metallic the sample is, and the optical properties calculations evaluate the absorption and reflectivity of the sample over a range of wavelengths. These results connect the changes in the structure to differences in metallicity and reflectivity and provide insights into observations in experiments.