Crystal Surface Reconstruction And Relaxation Of The Theoretical Analysis

The properties and functions of the material are closely relate to the arrangement of the surface structure, and the material surface is the first area where the physical and chemical properties have been changed. So we must first attention the surface structure when study the properties and functions. The arrangement of the surface structure is different from the bulk for the crystal material which lead to atoms near the surface will move up and down to a new environment and readjust to lower their kinetic energy. The research in the arrangement of surface structure and surface energy are the foundation for the knowledge of materials and then enable us to change one of their properties even to design new type of materials. In this paper, the surface reconstruction and relaxation for Fcc metals have been studied by using the modified embedded-atom method and Vienna ab-initio simulation package (VASP) of first-principle within the framework of density functional theory. The research can be divided into two parts:(1) With modified embedded-atom method (MEAM), the surface energy of the perfect and (1×2) missing row structure on (100), (110) and (111) surfaces, and (1×3), (1×4) and (1x5) missing row structure on (110) surface have been calculated for ten FCC metals Pb, Au, Pt, Ir, Ag, Pd, Rh, Cu, Ni and Al. According to the energy minimization, we know that the (1×2) missing row reconstruction cannot be formed naturally on (100) and (111) surfaces of all ten FCC metals. However, not only (1×2) but also (1×3) missing row reconstruction can be formed on (110) surface of Au, Pt and Al spontaneously. These are consistent with the experimental results except Al for which the experiment has not been reported. In addition to the surface energy explanation, the results are also analyzed in terms of the surface configurations and valence electron structures.The results found that, The MR reconstruction can occur when d bonds overlap between surface atoms to form new d-d bonds. the possibility of forming the d-d bonds between surface atoms and therefore the MR reconstruction decreases for 5d, 4d and 3d metals as well. It also relates to the facets which construct the surface and the including angle.(2) The lattice constant a₀, surface energies and multilayer relaxations on low index surfaces (100), (110) and (111) of metal Pt have been calculated by Vienna ab-initio simulation package (VASP) of first-principle within the framework of density functional theory. The results found that, before and after relaxation, the surfaces energies are E₁₁₁100110. The heavy relaxations are occur on first two layers, the relaxations decrease oscillatory with the surface thickness increase, and the relaxation magnitude of first interlayer space on (100), (110) and (111) are |△d₁₁₁|<|△d₁₀₀|<|△d₁₁₀|- The results also show that (100) and (110) surfaces are inward relaxation, while (111) surface is outward relaxation. The results are good agreement with the experiment. In addition, the densities of states (DOS) have been analysed before and after relaxation, the d partial density of states are very different from the bulk, before and after relaxation, the variation of The d partial density of states are occur on first two interpalce. After relaxation, on (100) and (110) surfaces, The d partial density of states decrease on high energy state and increase on lowe energy state. While on (111) surface the d partial density of states increse on high energy state and decrease on lowe energy state. This may be due to the inward relaxation on (100) and (110) surfaces while outward relaxtion on (111) surface.