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地球物理学的基础研究中发挥着重要的作用，而且在合成环境压力下不可接近的亚稳晶体方面也有着重要的应用。然而，在超高压条件下对少量试样进行现场观测是非常困难的，因此计算机模拟的理论支持变得越来越重要。本工作旨在通过在传统的第一性原理分子动力学（FPMD）方法的形式中引入恒压格式，建立独立于实验的高压下预测材料晶体结构和电子性质的方法。我们利用共轭梯度技术开发了FPMD方法的并行计算机代码，用于优化电子结构。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。本计算机程序用于研究以下问题：(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异质金刚石的材料设计，即预测可能的结构及其性质；(3)碱掺杂c60聚合物的结构优化和大规模带计算(4)CaSi_2多晶稳定性的压力依赖性(5)寻找sn_4高压原子相的可能结构

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