Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
J Chem Phys. 2019 Feb 21;150(7):074506. doi: 10.1063/1.5079758.
We present an equation of state for the solid and liquid phases of lithium fluoride that covers a wide range of conditions from ambient pressure and temperature to the high pressures and temperatures exhibited in shock- and ramp-compression studies. The particular solid phase we have focused on in this work is the B1 phase. We have followed an approach where the pressure and heat-capacity functions of both phases are fit to experimental data and our own quantum molecular dynamics simulations and are then integrated in a thermodynamically consistent way to obtain the corresponding free-energy functions. This approach yields a two-phase equation of state that provides better overall agreement with experimental data than other equations of state for lithium fluoride, such as SESAME 7271v3, LEOS 2240, and the model presented by Smirnov. The last of these is a three-phase equation of state that predicts a B1-B2 transition along the shock Hugoniot at a pressure of about 140 GPa. This solid-solid transition has been a topic of speculation and debate in the literature for over 50 years, culminating in the work of Smirnov, who has developed the only potentially viable equation of state that allows for this transition. We explain why the proposed B1-B2 transition at 140 GPa is not consistent with recent velocimetry data.
我们提出了一个氟化锂的固液两相状态方程，该方程涵盖了从环境压力和温度到冲击和斜坡压缩研究中表现出的高压高温的广泛条件。在这项工作中，我们特别关注的是 B1 相。我们采用了一种方法，即分别拟合两相的压力和热容函数与实验数据和我们自己的量子分子动力学模拟数据，然后以热力学一致的方式进行积分，以获得相应的自由能函数。这种方法得到的两相状态方程与氟化锂的其他状态方程（如 SESAME 7271v3、LEOS 2240 和 Smirnov 提出的模型）相比，能更好地整体符合实验数据。最后一个模型是一个三相状态方程，它预测在约 140 GPa 的冲击 Hugoniot 上会发生 B1-B2 转变。这种固-固相变一直是文献中推测和争论的话题，最终 Smirnov 提出了唯一可能可行的允许这种转变的状态方程。我们解释了为什么在 140 GPa 处提出的 B1-B2 转变与最近的速度测量数据不一致。
