The large-scale molecular dynamics simulations have been performed to understand the microscopic mechanism governing the phase transition of solid hydrogen under the high-pressure compression. These results demonstrate that the face-centered-cubic-to-hexagonal close-packed phase transition is initiated first at the surfaces at a much lower pressure than in the volume and then extends gradually from the surface to volume in the solid hydrogen. The infrared spectra from the surface are revealed to exhibit a different pressure-dependent feature from those of the volume during the high-pressure compression. It is thus deduced that the weakening intramolecular H-H bonds are always accompanied by hardening surface phonons through strengthening the intermolecular H2-H2 coupling at the surfaces with respect to the counterparts in the volume at high pressures. This is just opposite to the conventional atomic crystals, in which the surface phonons are softening. The high-pressure compression has further been predic...

中文翻译：

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高压压缩下固体氢的表面引发相变

已经进行了大规模分子动力学模拟，以了解在高压压缩下控制固体氢相变的微观机制。这些结果表明，面心立方到六边形密堆积相变首先在比体积低得多的压力下在表面开始，然后在固体氢中从表面逐渐延伸到体积。来自表面的红外光谱显示出与高压压缩过程中体积的红外光谱不同的压力相关特征。因此推断，通过在高压下相对于体积中的对应物加强表面的分子间 H2-H2 耦合，减弱的分子内 HH 键总是伴随着硬化的表面声子。这与传统的原子晶体相反，其中表面声子正在软化。高压压缩进一步被预测...