高温高压下Na、Ba掺杂硅基笼状化合物性质的第一性原理研究

硅基笼状化合物及其衍生物以其良好的开放性在热电、超导、磁学、光伏材料、超硬材料和储氢材料等方面都有着诱人的应用前景，受到了越来越多研究者的关注。然而由于对其力学和热力学性质认识的不够，导致实验中在高温高压环境下很难合成单相好的样品。另外，关于Na、Ba等元素掺杂下硅基笼状化合物高压稳定性和相变的理论和实验研究还存在很多的争议和矛盾。本课题将基于第一性原理方法以Na、Ba掺杂硅基笼状化合物为代表研究高压下该系列笼状化合物的结构稳定性和相变以及热力学性质，采用最新发展的基于粒子群优化算法预测在高压下可能存在的新型Na-Si二元化合物，该项研究将有助于发现新型纳米笼状结构化合物，也为高温高压下有效合成该类化合物提供有益的理论参考。

Because of the special cage-like structure with good opening, silicon based clathrate compounds and their derivatives have received great attentions recently for the potential applications in thermoelectric, superconductivity, magnetics, photovoltaic material, super-hard material and even hydrogen storage material. However, the mechanical and thermodynamic stabilities of these compounds are not clear which makes difficult in experiments for a well-controlled single phase crystal growth under high pressure and high temperature. Moreover, there are many disputations and contradictions in the study of high pressure stabilities and phase transition of silicon based compounds with Ba and Na doped both theoretically and experimentally. In this work, we will study the stability of the lattice structure, phase transition and thermodynamic properties of these silicon based compounds with Ba and Na doped under high pressure and high temperature via first principle analysis, and the possible existence of new structure of Na-Si binary compounds are predicted as well through a new developed software CALYPSO. This study will be helpful to find new nanocage-like compounds and provide theoretical guidance for the efficient synthesis of these compounds..