Structures of solid hydrogen at 300 K
Structures of solid hydrogen at 300 K
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DOI：
10.1103/physrevb.101.094104
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发表时间：
2020-03-18
影响因子：
3.7
通讯作者：
Loveday, John S.
中科院分区：
文献类型：
--
作者：
Ackland, Graeme J.;Loveday, John S.
本文给出了室温下氢相变分子动力学模拟的x射线衍射图（XRD）。通过直接对原子成像和测量相关函数，可以很容易地在模拟中识别相变。结果表明，氢的I、III、IV和V相的室温XRD谱图非常相似。XRD的转变特征是弱峰和超晶格反射，表明六边形闭包（hcp） I相的对称性破坏，以及c/a比的明显变化。由分子动力学计算得到的XRD谱图与由结构搜索得到的静态最小焓结构的谱图有很大的不同。模拟还表明，在相I中，分子越来越局限于基面，并表明可能存在一个不寻常的临界点，终止相I- iii的边界线。根据这些结果，我们提出了一种范式转变，即密度泛函理论计算的预测应被视为最可能的假设。具体来说，我们表明最近的实验结果支持分子动力学模拟所提出的图像，并且与同结构hcp转化的解释不一致。
We present simulated x-ray diffraction patterns (XRD) from molecular dynamics studies of phase transformations in hydrogen at room temperature. Phase changes can be easily identified in simulation, by directly imaging the atoms and measuring correlation functions. We show that the room-temperature XRD patterns for hydrogen phases I, III, IV, and V are very similar. The signatures of the transformations in XRD are weak peaks and superlattice reflections denoting symmetry breaking from the hexagonal-closed-packed (hcp) phase I, and a pronounced change in the c/a ratio. The XRD patterns implied by molecular dynamics calculations are very different from those arising from the static minimum enthalpy structures found by structure searching. Simulations also show that within phase I, the molecules become increasingly confined to the basal plane and suggest the possibility of an unusual critical point terminating the phase I-III boundary line. With these results, we propose a paradigm shift, i.e., that the predictions from density functional theory calculations should be seen as the most likely hypothesis. Specifically, we show that recent experimental results support the picture advanced by molecular dynamics simulations, and are inconsistent with the interpretation of an isostructural hcp transformation.