Green's function molecular dynamics of semiconductor defects and surfaces

First-principles molecular dynamics studies are carried out in this Dissertation for semiconductor defects and surfaces. A real space Green's function technique based on crystalline tight-binding Hamiltonian is used for the force calculation in the dynamics.; The technique is applied for the first time here to study bulk defect problems. Special points are used in the k-space integration to calculate the Green's function (GF) of a perfect crystal bulk. It is found that even very small subspaces, appropriately chosen, can give excellent results. The convergence is much faster than that reported for other techniques.; For the diamond structure bulk with a point defect, a 41 atom real space Green's function is found to be sufficiently large to simulate an infinite crystal.; In surface problems, an effective method is developed to deal with complicated surface reconstruction by using sample cells which change their structures in the molecular dynamics (MD) in accordance with the forces calculated by the Green's function, and using the 2d periodicities. Two approximate approaches have been used to quicken the simulations.; By making use of the 2d symmetry in GFMD, a surface relaxation can be simulated with a very small sample cell (as long as it is bigger than one primitive cell). The advantage of our GFMD method has been illustrated by the efficient computation of surface relaxation with reasonable accuracy. Surface relaxations have been carried out for diamond, silicon and graphite surfaces. We have found geometries for diamond and silicon (001), (110) and (111) surfaces which are supported by experimental results.; GFMD has also been proposed as a means for studying the initial stages of intercalation in a layered material. Chemisorption on graphite c-face and a-face has been studied. The behavior of these layers has been examined in vaccum or with oxygen atoms above the c-face, in-between two layers, and above the a-face. The c-face is found to be stable with respect to incoming oxygen atoms in that graphitic bonds are not broken. When oxygen atoms are sandwiched between the graphite layers in the bulk, bonds are formed between oxygen atoms and carbon atoms of the two neighboring layers, but no graphitic bonds are broken. (Abstract shortened by UMI.)...