Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated systematically by using a first-principles calculations method based on the density functional ...Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated systematically by using a first-principles calculations method based on the density functional theory. The calculation results of adsorption energy and diffusion energy barrier show that hydrogen atom is apt to be adsorbed at fcc and hcp sites on clean Mg (0001) surface, and fcc adsorption site is found to be more preferred. The highest diffusion energy barrier is estimated as 0.6784 eV for the diffusion of hydrogen from clean Mg (0001) surface into its bulk. Surface effects, which affect hydrogen diffusion obviously, results in a slow diffusion velocity of hydrogen from surface to subsurface, while a fast one from subsurface to bulk, indicating the range of surface effects is only restricted within two topmost layers of Mg (0001) surface. Comparatively, Mg atom vacancy on Mg (0001) surface not only enhances the chemisorption interaction between H and Mg surface, but also benefits H atom diffusion in Mg bulk with relatively more diffusion paths compared with that of clean surface. Besides, hydrogen atom is found to occupy mostly the tetrahedral interstice when it diffuses into the Mg bulk. Further analysis of the density of states (DOS) shows that the system for hydrogen atom to be adsorbed at fcc site has a lower DOS value (N (EF)) at Fermi level and more bonding elec- trons at the energy range blow the Fermi level of H/Mg (0001) system as compared with that at hcp site. On the other hand, the enhanced chemisorption interaction between hydrogen and defective surface should be attributed to the fact that the electronic structures of Mg (0001) surface are modified by an Mg vacancy, and the bonding electrons of the topmost layer Mg atoms are transferred from low energy range to Fermi level, which is in favor of improving the surface activity of Mg (0001) surface.展开更多
The adsorption of low-coverage of F and Cl adatoms on the Mg（0001） surface was investigated using first-principles calculations based on the density functional theory（DFT）.The stability of the（2×2） structur...The adsorption of low-coverage of F and Cl adatoms on the Mg（0001） surface was investigated using first-principles calculations based on the density functional theory（DFT）.The stability of the（2×2） structures formed by halogen atoms adsorbed at different sites was determined.The difference between the adsorption of F and Cl on Mg（0001） surface was also discussed.The calculation results show that hollow sites are the energetically most favorable at the low-coverage.It can be concluded from the Mulliken charges and density of states that electrons transfer from the substrate Mg atoms to the adatoms,which leads to the formation of adsorbate bond and further causes the stronger interaction between Mg atom and adatom.The interaction between Cl and Mg atoms is weaker than the interaction between F and Mg.展开更多
基金Supported by the PhD Programs Foundation of Ministry of Education of China(Grant No.200805321032)the Science and Technology Program Project of Hunan Province(Grant No.2008GK3083)the Program for Changjiang Scholars and the Innovative Research Team in university(Grant No.531105050037)
文摘Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated systematically by using a first-principles calculations method based on the density functional theory. The calculation results of adsorption energy and diffusion energy barrier show that hydrogen atom is apt to be adsorbed at fcc and hcp sites on clean Mg (0001) surface, and fcc adsorption site is found to be more preferred. The highest diffusion energy barrier is estimated as 0.6784 eV for the diffusion of hydrogen from clean Mg (0001) surface into its bulk. Surface effects, which affect hydrogen diffusion obviously, results in a slow diffusion velocity of hydrogen from surface to subsurface, while a fast one from subsurface to bulk, indicating the range of surface effects is only restricted within two topmost layers of Mg (0001) surface. Comparatively, Mg atom vacancy on Mg (0001) surface not only enhances the chemisorption interaction between H and Mg surface, but also benefits H atom diffusion in Mg bulk with relatively more diffusion paths compared with that of clean surface. Besides, hydrogen atom is found to occupy mostly the tetrahedral interstice when it diffuses into the Mg bulk. Further analysis of the density of states (DOS) shows that the system for hydrogen atom to be adsorbed at fcc site has a lower DOS value (N (EF)) at Fermi level and more bonding elec- trons at the energy range blow the Fermi level of H/Mg (0001) system as compared with that at hcp site. On the other hand, the enhanced chemisorption interaction between hydrogen and defective surface should be attributed to the fact that the electronic structures of Mg (0001) surface are modified by an Mg vacancy, and the bonding electrons of the topmost layer Mg atoms are transferred from low energy range to Fermi level, which is in favor of improving the surface activity of Mg (0001) surface.
基金Project (51201079) supported by the National Natural Science Foundation of ChinaProject (2012Z099) supported by the Scientific Research Fund of Department of Education of Yunnan Province,ChinaProject (KKSY201251033) supported by the Scientific Research Foundation for Introduced Talents of KMUST,China
文摘The adsorption of low-coverage of F and Cl adatoms on the Mg（0001） surface was investigated using first-principles calculations based on the density functional theory（DFT）.The stability of the（2×2） structures formed by halogen atoms adsorbed at different sites was determined.The difference between the adsorption of F and Cl on Mg（0001） surface was also discussed.The calculation results show that hollow sites are the energetically most favorable at the low-coverage.It can be concluded from the Mulliken charges and density of states that electrons transfer from the substrate Mg atoms to the adatoms,which leads to the formation of adsorbate bond and further causes the stronger interaction between Mg atom and adatom.The interaction between Cl and Mg atoms is weaker than the interaction between F and Mg.
基金Supported by Hunan Provincial Innovation Foundation for Postgraduate (521298294)Natural Science Foundation of Hunan Province (09JJ6079)Program for Changjiang Scholars and the Innovative Research Team in University (531105050037)
