First principle study of hydrogen diffusion in equilibrium rutile, rutile with deformation twins and fluorite polymorph of Mg hydride

► Diffusion barrier is lower in twin defects and fluorite polymorph then in rutile. ► Calculated hopping rates follow the same trend as the activation barriers. ► Hydrogen vacancies are more easily formed when they are clustered together. ► Activation barriers decrease if concentration of vacancies increases in MgH2.