Loa Ingo, Landgren Filip
SUPA, School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3FD, United Kingdom.
J Phys Condens Matter. 2024 Feb 7;36(18). doi: 10.1088/1361-648X/ad1e08.
Solid hydrogen is expected to become a monatomic metal under sufficiently high compression. With hydrogen having only a single valence electron and no ion core, the nature of x-ray diffraction patterns from the electron gas of monatomic metallic hydrogen is uncertain, and it is unclear whether they may yield enough information for a crystal structure determination. With emphasis on the Cs-IV-type (I41/amd) structure predicted for hydrogen at ∼500 GPa, the electron density distributions, zero-point and thermal atomic motion, and x-ray diffraction intensities are determined from first-principles calculations for several candidate phases of metallic hydrogen. It is shown that the electron distribution is much more structured than might be expected from the commonly employed free-electron-gas picture, and in fact more modulated than what is obtained from the superposition of free-atom charge densities. We demonstrate that an identification of the crystal structure of monatomic metallic hydrogen from x-ray diffraction is fundamentally possible and discuss the possibility of single-crystal diffraction from metallic hydrogen. An atomic scattering factor for the hydrogen atom in monatomic metallic hydrogen is constructed to aid the quantitative analysis of diffraction intensities from future x-ray diffraction experiments.
预计在足够高的压力下，固态氢会变成单原子金属。由于氢只有一个价电子且没有离子芯，单原子金属氢电子气的X射线衍射图案的性质尚不确定，而且不清楚这些图案是否能产生足够的信息来确定晶体结构。着重讨论了在约500吉帕压力下氢所预测的Cs-IV型（I41/amd）结构，通过第一性原理计算确定了金属氢几个候选相的电子密度分布、零点和热原子运动以及X射线衍射强度。结果表明，电子分布比常用的自由电子气模型所预期的要更具结构性，实际上其调制程度比自由原子电荷密度叠加所得到的还要高。我们证明从X射线衍射确定单原子金属氢的晶体结构在根本上是可行的，并讨论了从金属氢进行单晶衍射的可能性。构建了单原子金属氢中氢原子的原子散射因子，以辅助对未来X射线衍射实验的衍射强度进行定量分析。
