Equilibrium properties of hydrogen-helium mixtures under conditions similarto the interior of giant gas planets are studied by means of first principledensity functional molecular dynamics simulations. We investigate the molecularand atomic fluid phase of hydrogen with and without the presence of helium fordensities between $\rho=0.19$ g$ $cm$^{-3}$ and $\rho=0.66$ g$ $cm$^{-3}$ andtemperatures from $T=500 $K to $T=8000 {K}$. Helium has a crucial influence onthe ionic and electronic structure of the liquid. Hydrogen molecule bonds areshortened as well as strengthened which leads to more stable hydrogen moleculescompared to pure hydrogen for the same thermodynamic conditions. The {\it abinitio} treatment of the mixture enables us to investigate the validity of thewidely used linear mixing approximation. We find deviations of up to 8% inenergy and volume from linear mixing at constant pressure in the region ofmolecular dissociation.
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机译：通过第一原理密度泛函分子动力学模拟研究了氢-氦混合物在类似于巨型气体行星内部的条件下的平衡性质。我们研究了在有和没有氦气密度的情况下，氢的分子和原子流体相在$ \ rho = 0.19 $ g $ $ cm $ ^ {-3} $和$ \ rho = 0.66 $ g $ $ cm $ ^ {- 3} $，温度从$ T = 500 $ K到$ T = 8000 {K} $。氦气对液体的离子和电子结构具有至关重要的影响。在相同的热力学条件下，氢分子键的缩短和增强导致与纯氢相比更稳定的氢分子。混合物的{\ itbinitio}处理使我们能够研究广泛使用的线性混合逼近的有效性。我们发现恒定解离下分子解离区域中线性混合的能量和体积偏差高达8％。
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