Stopper Daniel, Hansen-Goos Hendrik, Roth Roland, Evans Robert
Institute for Theoretical Physics, University of Tübingen, Auf der Morgenstelle 14, 72076 Tübingen, Germany.
H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1 TL, United Kingdom.
J Chem Phys. 2019 Jul 7;151(1):014501. doi: 10.1063/1.5110044.
We revisit the competition between attractive and repulsive interparticle forces in simple fluids and how this governs and connects the macroscopic phase behavior and structural properties, as manifested in pair correlation functions. We focus on the asymptotic decay of the total correlation function h(r) which is, in turn, controlled by the form of the pair direct correlation function c(r). The decay of rh(r) to zero can be exponential (monotonic) if attraction dominates repulsion and exponentially damped oscillatory otherwise. The Fisher-Widom (FW) line separates the phase diagram into two regions characterized by the two different types of asymptotic decays. We show that there is a new and physically intuitive thermodynamic criterion which approximates well the actual FW line. This new criterion defines a line where the isothermal compressibility takes its ideal gas value χ=χ . We test our hypothesis by considering four commonly used models for simple fluids. In all cases, the new criterion yields a line in the phase diagram that is close to the actual FW line for the thermodynamic state points that are most relevant. We also investigate (Widom) lines of maximal correlation length, emphasizing the importance of distinguishing between the true and Ornstein-Zernike correlation lengths.
我们重新审视简单流体中吸引性和排斥性粒子间力的竞争，以及这种竞争如何支配并连接宏观相行为和结构性质，这在对关联函数中有所体现。我们关注总关联函数h(r)的渐近衰减，而它又由对直接关联函数c(r)的形式所控制。如果吸引力主导排斥力，rh(r)衰减至零可以是指数形式（单调的），否则就是指数衰减振荡形式。费希尔 - 威多姆（FW）线将相图分为两个区域（由两种不同类型的渐近衰减表征）。我们表明存在一个新的且物理直观的热力学判据，它能很好地逼近实际的FW线。这个新判据定义了一条等温压缩率取其理想气体值χ = χ 的线。我们通过考虑四种常用的简单流体模型来检验我们的假设。在所有情况下，对于最相关的热力学状态点，新判据在相图中给出的线都接近实际的FW线。我们还研究了（威多姆）最大关联长度线，强调区分真实关联长度和奥恩斯坦 - 泽尔尼克关联长度的重要性。
