We investigate the behavior of amorphous silicon under hydrostatic compression using molecular simulations. During compression, amorphous silicon undergoes a discontinuous nonequilibrium transition from a low-density to a high-density structure at a pressure of around $13$-$16$~GPa. Ensemble-averaged density and elastic constants change discontinuously across the transition. Densification of individual glassy samples occurs through a series of discrete plastic events, each of which is accompanied by a vanishing shear modulus. This is the signature of a series of elastic instabilities, similar to shear transformation zones observed during shear yielding of glasses. We compare the structure obtained during compression with a near-equilibrium form of amorphous silicon obtained by quenching a melt at constant pressure. This gives structures identical to nonequilibrium compression at low and high pressure, but the transition between them occurs gradually rather than discontinuously. Our observations indicate that the polyamorphic transition is of a nonequilibrium nature, and it has the characteristics of a yield transition that occurs under compression instead of shear.

中文翻译：

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压缩屈服和硅中的多晶转变

我们使用分子模拟研究了非晶硅在静水压缩下的行为。在压缩过程中，非晶硅在大约 $13$-$16$~GPa 的压力下经历从低密度结构到高密度结构的不连续非平衡转变。整体平均密度和弹性常数在过渡过程中不连续变化。单个玻璃样品的致密化通过一系列离散的塑性事件发生，每个事件都伴随着消失的剪切模量。这是一系列弹性不稳定性的特征，类似于玻璃剪切屈服期间观察到的剪切转变区。我们将压缩过程中获得的结构与通过在恒定压力下淬火熔体获得的近平衡形式的非晶硅进行比较。这给出了与低压和高压下的非平衡压缩相同的结构，但它们之间的过渡是逐渐发生的而不是不连续的。我们的观察表明多晶相转变具有非平衡性质，并且它具有在压缩而不是剪切下发生的屈服转变的特征。