Prediction of crystal structures on the basis of the interatomic forces

我们项目的目标是建设和发展“下个世纪的矿物学”。我们把精力集中在二氧化硅矿物上，我们的成果被国外科学界和新闻界评价为“卓越的”。主要成就如下：得到了SiO_2体系的第一原理对势（Tsuneyuki et al., 1988）。将电位参数放入Nose博士开发的恒压-温分子动力学程序中，1)压力诱导的石英和方晶石的非晶化，2)石英的低-高转变，以及3)硅熔体在压力下的粘度下降可以成功地重现，并在原子尺度上揭示了这些机制（Tsuneyuki et al.， 1989和1990）。2. 通过使用全势线性增广平面波近似的局部密度泛函计算（Park et al., 1988），表明在非常高的压力下，比金红石结构的硅多晶石密度更大的硅多晶石是稳定的。3. 在石英和方英石的高压加载计算机实验中，发现了几种硅原子以四、六重配位共存为特征的SiO_2新结构（并进行了晶体学描述）。这表明“新型”结构化合物可能通过热力学非平衡反应而不是通常的平衡反应获得（Tsuneyuki et al., 1990; Tsuchida and Yagi, 1989）。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）的开发尚未完成；这是最紧迫的任务，目前的计划不得不将其推迟。

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.