Quantum Monte Carlo study of the phase diagram of solid molecular hydrogen at extreme pressures.
Quantum Monte Carlo study of the phase diagram of solid molecular hydrogen at extreme pressures.
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DOI：
10.1038/ncomms8794
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发表时间：
2015-07-28
影响因子：
16.6
通讯作者：
Needs RJ
中科院分区：
文献类型：
--
作者：
Drummond ND;Monserrat B;Lloyd-Williams JH;López Ríos P;Pickard CJ;Needs RJ
建立氢的相图是实验物理和理论物理的一个重大挑战。单靠实验无法建立高压下固态氢的原子结构，因为氢对X射线的散射很弱。相反，我们对原子结构的理解主要基于密度泛函理论（DFT）。通过比较拉曼光谱中发现的低能量结构的DFT搜索与实验光谱，候选原子结构已被确定为每个实验观察到的阶段。不幸的是，DFT预测金属结构在高达400 GPa的广泛压力范围内具有能量优势，其中实验已知氢是非金属的。在这里，我们表明，更先进的理论方法（扩散量子蒙特卡罗计算）发现金属结构是没有竞争力的，并预测相图与实验合理的协议。这大大加强了候选原子结构准确地模拟实验观察到的相位的说法。 高压下氢的实验研究具有挑战性，因此理论是理解其相行为的核心;然而，计算的相图与以前的测量结果不一致。在这里，作者使用量子蒙特卡罗方法，并提出与实验定性一致的结果。
Establishing the phase diagram of hydrogen is a major challenge for experimental and theoretical physics. Experiment alone cannot establish the atomic structure of solid hydrogen at high pressure, because hydrogen scatters X-rays only weakly. Instead, our understanding of the atomic structure is largely based on density functional theory (DFT). By comparing Raman spectra for low-energy structures found in DFT searches with experimental spectra, candidate atomic structures have been identified for each experimentally observed phase. Unfortunately, DFT predicts a metallic structure to be energetically favoured at a broad range of pressures up to 400 GPa, where it is known experimentally that hydrogen is non-metallic. Here we show that more advanced theoretical methods (diffusion quantum Monte Carlo calculations) find the metallic structure to be uncompetitive, and predict a phase diagram in reasonable agreement with experiment. This greatly strengthens the claim that the candidate atomic structures accurately model the experimentally observed phases. Experimental studies of hydrogen at high pressure are challenging, so theory is central to understanding its phase behaviour; however, computed phase diagrams do not agree with previous measurements. Here, the authors use a quantum Monte Carlo method and present results in qualitative agreement with experiment.