We use density functional theory (DFT) and structure searching methods to show that the ground state of elemental sulfur is a barium-IVa type incommensurate host-guest (HG) phase between 386 and 679 GPa, becoming the first group-VI element predicted to possess such a structure. Within the HG phase, sulfur undergoes a series of transitions in which adjacent guest chains are not aligned but rather offset by different amounts, which can be described as a rearrangement of the stacking order of the chains. We show that these chain rearrangements are intimately coupled to modulations of the host and guest atoms, which prove crucial to stabilizing the HG structure. Unlike the high-pressure HG phases of other elements, sulfur does not exhibit interstitial charge localization, and instead features strongly localized “voids” that are depleted of electronic charge. Prior to adopting the HG structure, we predict that sulfur possesses an orthorhombic structure of $Fdd2$ symmetry. We calculate the superconducting critical temperatures of these newly discovered phases, and we show that $T_c$ is expected to peak between 24.8 and 28.2 K at 271 GPa.

中文翻译：

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压缩元素硫中超导不相称的主客体相

我们使用密度泛函理论 (DFT) 和结构搜索方法证明元素硫的基态是 386 到 679 GPa 之间的钡-IVa 型不公度主客体 (HG) 相，成为第一个预测为拥有这样的结构。在 HG 相内，硫经历了一系列转变，其中相邻的客链没有对齐而是偏移了不同的数量，这可以描述为链的堆叠顺序的重新排列。我们表明，这些链重排与主体和客体原子的调制密切相关，这对稳定 HG 结构至关重要。与其他元素的高压 HG 相不同，硫不表现出间隙电荷局部化，而是具有强烈局部化的“空隙”，这些“空隙”耗尽了电子。在采用 HG 结构之前，我们预测硫具有正交结构$Fdd2$对称。我们计算了这些新发现的相的超导临界温度，并表明${吨}_C$ 预计在 271 GPa 的 24.8 和 28.2 K 之间达到峰值。