Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854-8019, USA.
TCM Group, Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
Phys Rev Lett. 2018 Jun 22;120(25):255701. doi: 10.1103/PhysRevLett.120.255701.
A new phase V of hydrogen was recently claimed in experiments above 325 GPa and 300 K. Because of the extremely small sample size at such record pressures the measurements were limited to Raman spectroscopy. The experimental data on increase of pressure show decreasing Raman activity and darkening of the sample, which suggests band gap closure and impending molecular dissociation, but no definite conclusions could be reached. Furthermore, the available data are insufficient to determine the structure of phase V, which remains unknown. Introducing saddle-point ab initio random structure searching, we find several new structural candidates of hydrogen which could describe the observed properties of phase V. We investigate hydrogen metallization in the proposed candidate structures, and demonstrate that smaller band gaps are associated with longer bond lengths. We conclude that phase V is a stepping stone towards metallization.
最近在 325GPa 以上和 300K 的实验中声称出现了第五相氢。由于在如此高的压力下，样品的数量非常小，因此测量仅限于拉曼光谱。关于压力增加的实验数据表明，拉曼活性降低，样品变暗，这表明带隙闭合和即将发生的分子离解，但没有得出明确的结论。此外，可用的数据不足以确定第五相的结构，这仍然未知。引入鞍点从头算随机结构搜索，我们发现了几种新的氢结构候选物，它们可以描述第五相的观察到的性质。我们研究了所提出的候选结构中氢的金属化，并证明较小的带隙与较长的键长有关。我们得出结论，第五相是金属化的踏脚石。
