Modellingthe effect of pressure on the critical shear stress of MgO single crystalsAbstract:We use a hierarchical multi-scale model to study the effect of high pressure on the critical shear stresses of MgO. The two main slip systems, ½<110>{110} and ½<110>{100} are considered. Based on a generalized Peierls-Nabarro model, we show that the core structure of ½<110> screw dislocations is strongly sensitive to pressure. Mostly planar and spread in {110} at ambient pressure, the core of screw dislocations tends to spread in {100} with increasing pressure. Subsequently, one observesan inversion of the easiest slip systems between 30 and 60 GPa. At high pressure, the plasticity of MgO single crystals is expected to be controlled by ½<110>{100} slip systems, except at high temperature where both slip systems become active. Pressure isalso found to increase the critical resolved shear stresses and to shift the athermal temperature toward higher temperatures. Under high pressure, MgO is thus characterized by a significant lattice friction on both slip systems.