Do the atoms at second layer block the path of vacancies in the bulk? - The DFT study of vacancies below the Mg (0001) surface

Abstract

The formation energy of monovacancy and binding energy of divacancy at and below Mg (0001) surface are examined by ab initio calculations based on the density-functional theory. Appropriate dense of k-point mesh and large supercell is used to obtain reasonable values. During calculation, we find that higher formation energy is needed to form monovacancy at the second layer. The electron density contour plots shows that electron tends to accumulate in the vicinity of vacancy at the second layer and accumulation charges are also impact on the stableness of the divacancies located at different layers. The migration barrier energy of transition state for the vacancy at the second layer is counted to be very low because of the accumulation electrons apply the power to make the vacancy to migrate. Perhaps, our computational results will be useful to account for the diffusion of hydrogen atoms at bulk of Mg and the mechanism of catalysis of impurities like carbon for the diffusion of hydrogen atoms.