We employ first-principles molecular dynamics simulations to provide equation-of-state data, pair distribution functions (PDFs), diffusion coefficients, and band gaps of a mixture of hydrogen and methane under planetary interior conditions as relevant for Uranus, Neptune, and similar icy exoplanets. We test the linear mixing approximation, which is fulfilled within a few percent for the chosen P–T conditions. Evaluation of the PDFs reveals that methane molecules dissociate into carbon clusters and free hydrogen atoms at temperatures greater than 3000 K. At high temperatures, the clusters are found to be short-lived. Furthermore, we calculate the electrical conductivity from which we derive the non-metal-to-metal transition region of the mixture. We also calculate the electrical conductivity along the P–T profile of Uranus [N. Nettelmann et al., Planet. Space Sci., 2013, 77, 143–151] and observe the transition of the mixture from a molecular to an atomic fluid as a function of the radius of the planet. The density and temperature ranges chosen in our study can be achieved using dynamic shock compression experiments and seek to aid such future experiments. Our work also provides a relevant data set for a better understanding of the interior, evolution, luminosity, and magnetic field of the ice giants in our solar system and beyond.

中文翻译：

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行星内部条件下氢和甲烷的混合物

我们采用第一原理分子动力学模拟来提供与天王星、海王星和类似行星相关的行星内部条件下氢和甲烷混合物的状态方程数据、对分布函数 (PDF)、扩散系数和带隙冰冷的系外行星。我们测试了线性混合近似，对于所选的P – T条件，该近似在几个百分点内得到满足。对 PDF 的评估表明，在高于 3000 K 的温度下，甲烷分子会分解成碳簇和游离氢原子。在高温下，这些簇的寿命很短。此外，我们还计算了电导率，从中得出混合物的非金属到金属的过渡区域。我们还计算了天王星P-T剖面上的电导率[N.内特尔曼等人。，行星。空间科学。 , 2013, 77 , 143–151] 并观察混合物从分子流体到原子流体的转变作为行星半径的函数。我们研究中选择的密度和温度范围可以通过动态冲击压缩实验来实现，并寻求帮助未来的此类实验。我们的工作还提供了相关数据集，以便更好地了解太阳系及其他地区冰巨星的内部、演化、光度和磁场。