First Principle Study of Surface Structure and Elementary Process of Crystal Growth

阐明外延生长的微观基本过程，被认为是生长高度可控的晶体和超晶格的关键。我们的课题是同时优化电子态和原子排列，以阐明吸附的关键因素。我们运用密度泛函理论和分子动力学，用共轭梯度法进行优化。硅原子在硅（100）表面的吸附能是通过优化吸附原子与衬底中原子的坐标来确定的。我们确定了表面扩散势垒在二聚体方向上为2.0eV，在二聚体方向上为0.6eV。对阶梯流动机理进行了模拟，得到了与实验结果一致的结果。我们在类似的理论框架下研究了砷化镓表面硫原子钝化和金刚石在氢气氛中薄膜生长的问题。表面与晶体具有较强的各向异性。我们还研究了具有大各向异性的体系。Nakao和Fujita对插层化合物C_4KH_X进行了第一原理波段计算，并对方形晶格中的Hubbard模型进行了自旋密度波分析。平本阐明了电子-电子相互作用对一维准周期体系电子结构的影响。

To clarify the microscopic elementary processes of epitaxial growth, is considered to be a key for growing highly controlled crystals and superlattices. Our subject is the simultaneous optimization of the electronic states and the atomic arrangements to clarify the key factor of the adsorption.We used the density functional theory and the molecular dynamics, with the conjugate gradient method for optimization. Adsorption energy of Si adatom on the Si(100) surface is determined by optimizing the coordinates of the adsorption atom, and the atoms in the substrate. We determined that the potential barrier of the surface diffusion to be 2.0eV in the dimer direction and 0.6eV in the perpendicular to it. We made simulation of step flow mechanism and obtained the results consistent with the experiments. We are investigating the problems of the passivation of the GaAs surface by sulfur atoms and thin film growth of diamond in hydrogen atmosphere in a similar theoretical framework.Surface is different from the crystal in strong anisotropy. We also studied the systems with large anisotropy. Nakao and Fujita perfoiw the first principle band calculation of intercalation compound C_4KH_X and spin-density-wave analysis of the Hubbard model in the square lattice. Hiramoto clarified the effect of electron-electron interaction on the elctronic structure of the one dimensional quasi periodic system.