标题： 变形、晶格不稳定性以及在一般应用应力张量下的固态结构转变中的金属化现象：以Si I → Si II为例 显示英文标题

标题： Deformation, lattice instability, and metallization during solid-solid structural transformations under general applied stress tensor: example of Si I -> Si II

摘要： 密度泛函理论（DFT）被用于研究当半导体Si I（立方A4）和金属Si II（四角A5结构）在受到一般应力张量作用时的应力-应变行为、弹性不稳定性以及金属化现象。 在沿$\left<110 \right>$、$\left<1\bar{1}0 \right>$和$\left<001\right>$分别作用的正应力（$\sigma_1$、$\sigma_2$、$\sigma_3$）规定模拟单元的情况下，我们确定了6种独立应力的组合，这些组合会引发Si I$\rightarrow$Si II相变的晶格不稳定性以及半导体-金属电子转变。 金属化发生在结构相变之前，因此，受压的Si I可以是金属。 令人惊讶的是，在DFT中，无应力的Si II是亚稳态的。 值得注意的是，对于静水压力，相变发生在75.81 GPa，而在单轴应力下为11.03 GPa（或3.68 GPa平均压力）。 我们的主要结果：Si I→Si II相变由修正的转变功的临界值描述，如通过相场方法所发现的，且相变准则对于一般的施加应力只有两个参数。 更普遍地说，我们的发现对于揭示在受控和可预测的非静水加载和塑性变形下新或已知高压相的新颖（和更经济）材料合成路线至关重要。 显示英文摘要

摘要： Density functional theory (DFT) was employed to study the stress-strain behavior, elastic instabilities, and metallization during a solid-solid phase transformation (PT) between semiconducting Si I (cubic A4) and metallic Si II (tetragonal A5 structure) when subjected to a general stress tensor. With normal stresses ($\sigma_1$, $\sigma_2$, $\sigma_3$) acting along $\left<110 \right>$, $\left<1\bar{1}0 \right>$, and $\left<001\right>$, respectively, dictating the simulation cell, we determine combinations of 6 independent stresses that drive a lattice instability for the Si I$\rightarrow$Si II PT, and a semiconductor-metal electronic transition. Metallization precedes the structural PT, hence, a stressed Si I can be a metal. Surprisingly, a stress-free Si II is metastable in DFT. Notably, the PT for hydrostatic pressures is at 75.81 GPa, while under uniaxial stress it is 11.03 GPa (or 3.68 GPa mean pressure). Our key result: The Si I -> Si II PT is described by a critical value of the modified transformation work, as found with a phase-field method, and the PT criterion has only two parameters for a general applied stress. More generally, our findings are crucial for revealing novel (and more economic) material synthesis routes for new or known high-pressure phases under controlled and predictable non-hydrostatic loading and plastic deformation.