Analysis And Calculation Of Surface Energy With The Empirical Electron Theory In Solid And Molecule

Surface science occupies an important place in the research fields of solid science. And surface energy, one of the basic quantities in surface science, plays an important role in several physical and chemical processes. However, surface energies of solid are difficult to determine experimentally. And most theoretical methods, based on first principles or semi-empirical method, need further improvement.Based on the empirical electron theory (EET) in solid and molecule and the basic principle of surface science, this thesis puts forward a new surface model which is described as empirical electron surface model (EESM). Its main contents include five parts as follows:(1) the dangling bond analysis method (DBAM) which was used to investigate the numbers and the types of the bond between two neighbor crystal planes, in other word to analyze the contribution of the covalent electrons to the surface energy; (2) the Zp method which was used to analyze the contribution of the lattice electrons to the surface energy; (3) the dangling bond covalent electron density of surface which has a great influence on surface energy of various index surfaces; (4) surface valence electron structure (SVES) for describing the atomic hybridization state in the surface region; (5) mirror bond length difference (MBLD) used to analyze and calculate SVES.We have use EESM to establish a database of surface energy for various index surface of 12 hexagonal close-packed (hcp) metals,13 body-centred cubic (bcc) metals,12 face-centred cubic (fcc) metals,4 diamond cubic crystals, and 19 compounds with zinc blende structure. Under the first order approximation, these calculated surface energy values are in agreement with experimental and other theoretical values. Therefore, these surface energies of the model have higher credibility. Such extensive results obtained with the same theoretical model, are useful to both theorists and experimentalists.And according to the analysis and calculation of surface energy of alkali metals and alkaline earth metals, we provide a new idea to analyze and discuss the contribution of the lattice electron to the surface energy of hcp, bcc, and fcc structure. For the three structure, the ratio (Zp) of the contribution of lattice electrons to surface energy and the contribution of lattice electrons to the crystal cohesive energy of one atom, which is related to atomicity of the related crystal plane with a finite area, the distribution of lattice electrons and the surface orientation, has been calculated in this thesis. These results can be used to the calculation of the more other materials with the same structure.The anisotropy of surface energy of these structures has been analyzed. Correlated analysis showed that the order of surface energy of various index surfaces of hcp-metals was related with the ratio of lattice constants(c/a). And the surface energy of the (001) crystal surface decrease gradually with increase of c/a, therefore the most possible orientation of outer surface of hcp-metals is (001) with large number of c/a. For the bcc-metals, the close-packed (110) surface energy is the lowest of these index surfaces. For the fcc-metals, the close-packed (111) surface energy is the lowest of these index surfaces. For the diamond cubic crystals and compounds with zinc blende structure, the surface energy order of the low index crystal planes is (001), (110), and (111). So the most probable surface for such crystals will be formation of free faces of (111) kind. And we have also analyzed the anisotropy of (hk0) type surfaces and (hhl) type surfaces of these two structures.The dangling bond covalent electron density of some index crystal surfaces has been calculated in this thesis. And it has a great influence on surface energy of various index surfaces and the anisotropy of surface. We have also analyzed the influence of lattice electron to the anisotropy of surface energy. Therefore, covalent electron and lattice electron codetermine the order of surface energy of various index surfaces.We have also analyzed SVES of silver with MBLD. And SVES may be extended to the analysis of surface relaxation, and even surface reconstruction, which pointes out the research direction and improvement direction of this new model.