Due to gravitational self-compression, the pressure in planetary interiors can reach millions of times the atmospheric pressure. Such high pressure has a significant influence on their rheology. In the present paper, we focus on how pressure in the range of the Earth's lower mantle may influence the structure of a MgO {310}/[001] tilt boundary. The defected structure of the grain boundary (GB) will be described through its dislocation, disclination, and generalized-disclination (g-disclination) density fields. At first, the strain and rotation fields in the boundary area at different pressures are derived from the discrete atomic positions simulated by first-principles calculations. For each pressure, the discontinuities of displacement, rotation, and strain in the boundary area are continuously rendered by dislocation, disclination, and g-disclination density fields, respectively. These density fields measured at different pressures are compared to provide understanding on how pressure does influence the GB structures in Earth materials.
