We consider a steady-state (but transient) situation in which a warm dense aggregate is a two-temperature system with equilibrium electrons at temperature Te, ions at Ti, and Te ≠ Ti. Such states are achievable by pump–probe experiments. For warm dense hydrogen in such a two-temperature situation, we investigate nuclear quantum effects (NQEs) on structure and thermodynamic properties, thereby delineating the limitations of ordinary ab initio molecular dynamics. We use path integral molecular dynamics (PIMD) simulations driven by orbital-free density functional theory (OFDFT) calculations with state-of-the-art noninteracting free-energy and exchange-correlation functionals for the explicit temperature dependence. We calibrate the OFDFT calculations against conventional (explicit orbitals) Kohn–Sham DFT. We find that when the ratio of the ionic thermal de Broglie wavelength to the mean interionic distance is larger than about 0.30, the ionic radial distribution function is meaningfully affected by the inclusion of NQEs. Moreover, NQEs induce a substantial increase in both the ionic and electronic pressures. This confirms the importance of NQEs for highly accurate equation-of-state data on highly driven hydrogen. For Te > 20 kK, increasing Te in the warm dense hydrogen has slight effects on the ionic radial distribution function and equation of state in the range of densities considered. In addition, we confirm that compared with thermostatted ring-polymer molecular dynamics, the primitive PIMD algorithm overestimates electronic pressures, a consequence of the overly localized ionic description from the primitive scheme.

中文翻译：

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两个温度温暖的稠密氢作为由无轨道密度泛函理论电子力驱动的量子质子的测试

我们考虑一种稳态（但瞬态）情况，其中温暖的致密聚集体是一个双温度系统，平衡电子在温度 Te，离子在 Ti，并且 Te ≠ Ti。这种状态可以通过泵-探针实验实现。对于在这种两种温度情况下的暖致密氢，我们研究了核量子效应 (NQE) 对结构和热力学性质的影响，从而描绘了普通从头算分子动力学的局限性。我们使用由无轨道密度泛函理论 (OFDFT) 计算驱动的路径积分分子动力学 (PIMD) 模拟，以及最先进的非相互作用自由能和交换相关函数，用于显式温度依赖性。我们针对常规（显式轨道）Kohn-Sham DFT 校准 OFDFT 计算。我们发现，当离子热德布罗意波长与平均离子间距的比值大于约 0.30 时，离子径向分布函数受到包含 NQE 的显着影响。此外，NQE 引起离子和电子压力的显着增加。这证实了 NQE 对于高度驱动氢的高精度状态方程数据的重要性。对于 Te > 20 kK，在热致密氢中增加 Te 对考虑的密度范围内的离子径向分布函数和状态方程有轻微影响。此外，我们证实，与恒温环聚合物分子动力学相比，原始 PIMD 算法高估了电子压力，这是原始方案过度局部化离子描述的结果。