什么是简单液体？
What constitutes a simple liquid?
摘要：
简单液体传统上被定义为经典粒子通过径向对称对势相互作用的多体系统。我们建议，一个简单的液体应该定义，而不是由具有较强的相关性的维里和势能平衡波动的NVT系综的属性。这两个定义之间有相当大的重叠，但也有一些显著的差异。例如，在新的定义中，简单性并不是分子间势的一个性质，因为液体通常只在其相图的一部分中强相关。此外，根据新定义，并非所有简单液体都是原子的（即，具有径向对称的对势），并且不是所有的原子液体都是简单的。本文的主要部分激发了液体简单性的新定义，提出了证据表明，液体是强相关的，当且仅当其分子间的相互作用可以忽略第一配位壳层（FCS）之外。这是证明了由NVT模拟的结构和动力学的15个原子和分子模型液体与转移力截止放置在第一个最小的径向分布函数。没有证据表明强关联性导致了化学表征，但它与强关联液体相图中存在同晶相是一致的。最后，我们注意到，简单液体的FCS表征质疑标准微扰理论的基础，根据该理论，排斥力和吸引力在液体物理中起着根本不同的作用。
英文摘要：
Simple liquids are traditionally defined as many-body systems of classical particles interacting via radially symmetric pair potentials. We suggest that a simple liquid should be defined instead by the property of having strong correlation between virial and potential energy equilibrium fluctuations in the NVT ensemble. There is considerable overlap between the two definitions, but also some notable differences. For instance, in the new definition simplicity is not a property of the intermolecular potential only because a liquid is usually only strongly correlating in part of its phase diagram. Moreover, according to the new definition not all simple liquids are atomic (i.e., with radially symmetric pair potentials) and not all atomic liquids are simple. The main part of the paper motivates the new definition of liquid simplicity by presenting evidence that a liquid is strongly correlating if and only if its intermolecular interactions may be ignored beyond the first coordination shell (FCS). This is demonstrated by NVT simulations of structure and dynamics of 15 atomic and molecular model liquids with a shifted-forces cutoff placed at the first minimum of the radial distribution function. No proof is given that the chemical characterization follows from the strong correlation property, but it is shown to be consistent with the existence of isomorphs in strongly correlating liquids' phase diagram. Finally, we note that the FCS characterization of simple liquids calls into question the basis for standard perturbation theory, according to which the repulsive and attractive forces play fundamentally different roles for the physics of liquids.
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