Prediction of crystal structures on the basis of the interatomic forces

我们项目的目标是建设和发展“即将到来的世纪的矿物学”。我们将精力集中在硅石矿物上，我们的成果被国外科学界和新闻界评价为“显著的成果”。主要成果如下：1.得到了SiO_2体系的第一主对势(Tsuneyuki等人，1988)。将势能参数放入Nose博士开发的恒压-温分子动力学程序中，1)石英和方石英的压力诱导非晶化，2)石英的低-高转变，3)硅熔体中压力下的粘度下降，并在原子尺度上揭示了机理(Tsuneyuki等人，1989和1990)。2.采用全势能线性缀加平面波近似的局域密度泛函计算表明，比(金红石结构)更致密的二氧化硅多晶型在很高的压力下是稳定的(Park等，1988)。3.在石英和方石英的高压加载计算机实验过程中，发现了SiO_2的几种新结构，其特征是硅原子以四配位和六配位共存，并对其进行了结晶学描述。这表明了通过热力学非平衡运行而不是通常的平衡运行来获得“新的”结构化合物的可能性(Tsuneyuki等人，1990年；Tsuhida和Yagi，)。由于时间的限制，量子力学分子动力学程序(Carr和Parinello提出的方法的扩展)的开发还没有完成；这是本项目不得不推迟的最紧迫的任务。

The aim of our project has been to construct and develop the "mineralogy of the coming century". We concentrated our effort on the silica minerals, and our results have been evaluated as of "remarkable ones" by scientific community and journalism abroad. Chief achievements are as following: 1. First-principle pair-potential for SiO_2 system was obtained (Tsuneyuki et al., 1988). Putting the potential parameters into a constant pressure-temperature molecular dynamics program developed by Dr. Nose, 1) pressure-induced amorphization in quartz and cristabaflite, 2) the low-high transition of quartz, and 3) viscosity decrease under pressures in silica melt could successfully reproduced and the mechanisms have been revealed in an atomistic scale (Tsuneyuki et al., 1989 and 1990). 2. A silica polymorph denser than stishovite (of the rutile structure) was shown to be stable at very high pressures by the local density funetional calculation using the full- potential linear augmented plane wave approximation (Park et al., 1988). 3. Several new structures of SiO_2, characterized by coexistence of Si atoms in four- and six-fold coordinations has been recognized (and crystallographically described) during the course of high-pressure loading computer experiment on quartz and cristobalite. This suggests the possibility that "novel" structured compounds may be obtained by thermodynamically non-equilibrated runs rather than usual, equilibrated runs(Tsuneyuki et al., 1990; Tsuchida and Yagi, 1989).Due to the limitation in time, development of quantum-mechanical molecular dynamics program (an extension of the methodology suggested by Carr and Parinello) has not been finished; this being the most urgent task which has to be postponed by the present project.