S Adsorption at Regular and Defect Sites of the MgO (001) Surface: Cluster Model Study at DFT Level
We have studied the adsorption of sulfur at regular and defect sites of the MgO (001) surface using cluster models embedded in a large array of point charges by the density functional method. The calculated results indicate that it is a chemical adsorption regarding sulfur at both the regular site and the defect site of the MgO (001) surface. Especially for sulfur adsorbed at different oxygen vacancy sites (F, F + and F 2+ centers) and different magnesium vacancy sites (V, V - and V 2- centers), it has very large adsorption energies, which reflects the fact that the MgO (001) surface with the vacancies is an excellent adsorbent for sulfur adsorption. Besides, we find that the adsorbed sulfur is almost inserted into the lattice for sulfur adsorbed at the magnesium vacancy site of the MgO (001) surface. The adsorption energy of sulfur on the MgO (001) surface with magnesium vacancies is much larger when compared to that on the MgO (001) surface with oxygen vacancies. At the same time, it is also found that the S behaves as an electron acceptor except that it is adsorbed at the magnesium vacancy site behaving as an electron donor.