压力电离引起的流体氦的热力学不稳定性
The Thermodynamical Instability Induced by Pressure Ionization in Fluid Helium
摘要：
本文以液氦为例，对化学图象中的压力电离进行了系统的研究。通过比较化学模型的各种变体，证明了压力电离的行为取决于自由能函数的构造。在库仑自由能采用Padé插值公式描述的化学模型中，发现由压力电离引起的热不稳定性表现为沿压力-密度曲线和压力-温度曲线的不连续下降或连续下降和上升，这与第一性原理模拟的流体氢的一级液-液相变非常相似.与此相反，在变体化学模型与库仑自由能项经验削弱，没有引起压力电离时，产生的状态方程的不稳定性，实现了良好的协议与流体氦的第一性原理模拟。
英文摘要：
A systematic study of pressure ionization is carried out in the chemical picture by the example of fluid helium. By comparing the variants of the chemical model, it is demonstrated that the behavior of pressure ionization depends on the construction of the free energy function. In the chemical model with the Coulomb free energy described by the Padé interpolation formula, thermodynamical instability induced by pressure ionization is found to be manifested by a discontinuous drop or a continuous fall and rise along the pressure-density curve as well as the pressure-temperature curve, which is very much like the first order liquid-liquid phase transition of fluid hydrogen from the first principles simulations. In contrast, in the variant chemical model with the Coulomb free energy term empirically weakened, no thermodynamical instability is induced when pressure ionization occurs, and the resulting equation of state achieves good agreement with the first principles simulations of fluid helium.
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