Levashov V A, Ryltsev R E, Chtchelkatchev N M
Technological Design Institute of Scientific Instrument Engineering, 630055, Novosibirsk, Russia.
Vereshchagin Institute for High Pressure Physics, Russian Academy of Sciences, 108840, Troitsk, Moscow, Russia.
J Phys Condens Matter. 2021 Jan 13;33(2):025403. doi: 10.1088/1361-648X/abb516.
An efficient description of the structures of liquids and, in particular, the structural changes that happen with liquids on supercooling remains to be a challenge. The systems composed of soft particles are especially interesting in this context because they often demonstrate non-trivial local orders that do not allow to introduce the concept of the nearest-neighbor shell. For this reason, the use of some methods, developed for the structure analysis of atomic liquids, is questionable for the soft-particle systems. Here we report about our investigations of the structure of the simple harmonic-repulsive liquid in 3D using the triple correlation function (TCF), i.e., the method that does not rely on the nearest neighbor concept. The liquid is considered at reduced pressure (P = 1.8) at which it exhibits remarkable stability against crystallization on cooling. It is demonstrated that the TCF allows addressing the development of the orientational correlations in the structures that do not allow drawing definite conclusions from the studies of the bond-orientational order parameters. Our results demonstrate that the orientational correlations, if measured by the heights of the peaks in the TCF, significantly increase on cooling. This rise in the orientational ordering is not captured properly by the Kirkwood's superposition approximation. Detailed considerations of the peaks' shapes in the TCF suggest the existence of a link between the orientational ordering and the slowdown of the system's dynamics. Our findings support the view that the development of the orientational correlations in liquids may play a significant role in the liquids' dynamics and that the considerations of the pair distribution function may not be sufficient to understand intuitively all the structural changes that happen with liquids on supercooling. In general, our results demonstrate that the considerations of the TCF are useful in the discussions of the liquid's structures beyond the pair density function and interpreting the results obtained with the bond-orientational order parameters.
对液体结构，尤其是过冷时液体发生的结构变化进行有效描述仍是一项挑战。在这种情况下，由软粒子组成的系统特别有趣，因为它们常常展现出复杂的局部有序性，这使得引入最近邻壳层的概念变得困难。因此，一些为原子液体结构分析而开发的方法在软粒子系统中的应用存在疑问。在此，我们报告了使用三重关联函数（TCF）对三维简单简谐排斥液体结构的研究，即该方法不依赖于最近邻概念。该液体在减压（P = 1.8）下被考虑，此时它在冷却时表现出显著的抗结晶稳定性。结果表明，TCF能够处理那些无法从键取向序参量研究中得出明确结论的结构中的取向关联发展情况。我们的结果表明，如果通过TCF中的峰高来衡量，取向关联在冷却时会显著增加。柯克伍德叠加近似无法正确捕捉这种取向有序性的增加。对TCF中峰形状的详细考虑表明，取向有序性与系统动力学减慢之间存在联系。我们的发现支持这样一种观点，即液体中取向关联的发展可能在液体动力学中发挥重要作用，并且对径向分布函数的考虑可能不足以直观地理解过冷时液体发生的所有结构变化。总体而言，我们的结果表明，对TCF的考虑在讨论超出对密度函数的液体结构以及解释用键取向序参量获得的结果时是有用的。
