School of Physics and Optoelectronic Engineering, Ludong University, Yantai 264025, People's Republic of China.
J Chem Phys. 2017 Nov 28;147(20):204501. doi: 10.1063/1.4999009.
Although the existence of liquid-liquid phase transition has become more and more convincing, whether it will terminate at a critical point and what is the order parameter are still open. To explore these questions, we revisit the fluid-liquid phase transition (FLPT) in phosphorus (P) and study its phase behavior by performing extensive first-principles molecular dynamics simulations. The FLPT observed in experiments is well reproduced, and a fluid-liquid critical point (FLCP) at T = 3000 ∼ 3500 K, P = 1.5-2.0 Kbar is found. With decreasing temperature from the FLCP along the transition line, the density difference (Δρ) between two coexisting phases first increases from zero and then anomalously decreases; however, the entropy difference (ΔS) continuously increases from zero. These features suggest that an order parameter containing contributions from both the density and the entropy is needed to describe the FLPT in P, and at least at low temperatures, the entropy, instead of the density, governs the FLPT.
尽管液相-液相相变的存在变得越来越有说服力，但它是否会在临界点终止以及什么是序参量仍未解决。为了探索这些问题，我们重新研究了磷（P）中的液-液相转变（FLPT），并通过进行广泛的第一性原理分子动力学模拟来研究其相行为。实验中观察到的 FLPT 得到了很好的再现，并且发现在 T = 3000 到 3500 K，P = 1.5 到 2.0 Kbar 的范围内存在流体-液体临界点（FLCP）。随着温度从 FLCP 沿着转变线降低，两个共存相之间的密度差（Δρ）先从零开始增加，然后异常减小；然而，熵差（ΔS）连续从零开始增加。这些特征表明，需要一个包含密度和熵贡献的序参量来描述 P 中的 FLPT，并且至少在低温下，熵而不是密度控制着 FLPT。
