在高压下形成新的层状结构：SiS $_2$
Creating new layered structures at high pressures: SiS$_2$
摘要：
古老而新颖的层状结构因其物理、电学和摩擦性能而受到越来越多的关注。SiS $_2$，与SiO $_2$、CO $_2$和CS $_2$等电子，是一种材料，其相在实验上已知高达6 GPa，表现出1D链状、2D层状和3D四面体结构。我们提出了高度预测$ab$ $initio$计算结合进化结构搜索和分子动力学模拟的结构和电子演化的硅$_2$高达100 GPa。令人惊讶的是，在4至最高达至少100 GPa之间出现了与空间群$P\bar{3}m1$八面体配位的高度稳定的CdIPDMATHABMM型层状结构.四面体-八面体转换在压缩时是自然预期的，不像这里通过边缘共享的SiS $_6$八面体单元在片层内连接而不是在片层之间连接而实现的分层特征。预测的相位是半导体的，在10 GPa下具有约2 eV的间接带隙，在压力下减小，直到金属化约40 GPa。层状相的鲁棒性表明可能在环境压力下恢复，其中计算的声子谱表明动态稳定性。甚至发现单个单层在分离时是动态稳定的，这表明它可能从本体$P\bar{3}m1$ -SiS $_2$剪切或剥离。
英文摘要：
Old and novel layered structures are attracting increasing attention for their physical, electronic, and frictional properties. SiS$_2$, isoelectronic to SiO$_2$, CO$_2$ and CS$_2$, is a material whose phases known experimentally up to 6 GPa exhibit 1D chain-like, 2D layered and 3D tetrahedral structures. We present highly predictive $ab$ $initio$ calculations combined with evolutionary structure search and molecular dynamics simulations of the structural and electronic evolution of SiS$_2$ up to 100 GPa. A highly stable CdI$_2$-type layered structure, which is octahedrally coordinated with space group $P\bar{3}m1$ surprisingly appears between 4 and up to at least 100 GPa. The tetrahedral-octahedral switch is naturally expected upon compression, unlike the layered character realized here by edge-sharing SiS$_6$ octahedral units connecting within but not among sheets. The predicted phase is semiconducting with an indirect band gap of about 2 eV at 10 GPa, decreasing under pressure until metallization around 40 GPa. The robustness of the layered phase suggests possible recovery at ambient pressure, where calculated phonon spectra indicate dynamical stability. Even a single monolayer is found to be dynamically stable in isolation, suggesting that it could possibly be sheared or exfoliated from bulk $P\bar{3}m1$-SiS$_2$.
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