Application of the First-Principles Molecular Dynamics Method to the Study of Condensed Matter Physics under High Pressure

高压实验不仅在凝聚态物理和电子物理的基础研究中起着重要作用，而且在合成常压下无法实现的亚稳晶体的应用中也起着重要作用。然而，在超高压下对少量试样进行现场观测通常是非常困难的，因此，通过计算机模拟来提供理论支持变得越来越重要。在传统的第一性原理分子动力学（FPMD）方法的基础上，引入恒压方案，建立了一种不依赖于实验的预测高压下材料晶体结构和电子性质的方法，并开发了一个基于共轭梯度技术的FPMD方法的并行计算程序。我们还设计了一种寻找结构转变或化学反应过程过渡态的新方法。本程序已用于以下问题的研究：（1）石墨-c-金刚石和石墨-h-金刚石结构转变活化能的比较;（2）BCN异质金刚石材料设计，即可能结构和性质的预测，以及合成途径的建议;（3）碱掺杂C_（60）聚合物的结构优化和大尺度能带计算;（4）CaSi_2多晶型稳定性的压力依赖性;（5）SnI_4高压原子相可能结构的探索

High-pressure experiment has playd important role not only in fundamental research of condensed matter physics and geophysics but also in applications for synthesizing metastable crystals inaccessible at ambient pressure. In-situ obsesrvation of a small amount of specimen at ultra high pressure is, however, very difficult in general, so that theoretical suppport by computer simulations is getting morre and more important. This work aim at establishing the method of predicting crystal structures and electronic properties of materials under high pressure independently of experiments by introducing the constant pressure scheme into the traditional formalism of the First-Principles Molecular Dynamics (FPMD) method.We developed a parallelized computer code of the FPMD method with the conjugate-gradient technique for optimizing electronic structure. We also devised a new method of searching for the transition state of structural transformataion or chemical reaction processes. This computer code has been used for investigation of the following problems :(1) Comparison of the activation energies for graphite-to-c-diamond and graphite-to-h-diamond structural transformations(2) Material design of BCN heterodaimond, that is, prediction of the probable structures and their properties, and also proposal of synthesis paths(3) Structural optimization and large-scale band calculation of alkali-doped C60-polymers(4) Pressure dependence of the stability of polymorphs of CaSi_2(5) Search for probable structures of the high-pressurer atomic phase of SnI_4