Pruteanu Ciprian G, Kirsz Marcin, Ackland Graeme J
Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3FD, United Kingdom.
J Phys Chem Lett. 2021 Dec 2;12(47):11609-11615. doi: 10.1021/acs.jpclett.1c03206. Epub 2021 Nov 23.
Recent studies on supercritical nitrogen revealed clear changes in structural markers and dynamical properties when the coordination number approaches its maximum value. The line in and space where these changes occur is referred to as the Frenkel line. Here, we qualitatively reproduce such changes in the supercritical regime using the popular "optimized potential for liquid simulation" (OPLS) classical force field for molecular dynamics. Unfortunately, at 160 K, OPLS nitrogen predicts sublimation rather than producing a liquid phase; therefore, we developed our own force field to achieve quantitative agreement with experimental data. We confirm the asymptotic behavior of the coordination number on crossing the Frenkel line and note an associated change in the diffusion constant, consistent with the non-rigid to rigid liquid-like character of the "transition". The simulations allow us to track the Frenkel line to subcritical temperatures and demonstrate that it terminates at the triple point. This establishes the experimentally measurable changes, which could unequivocally determine the Frenkel line in other systems.
最近关于超临界氮的研究表明，当配位数接近其最大值时，结构标记和动力学性质会发生明显变化。这些变化发生的( 和 空间中的线被称为弗伦克尔线。在这里，我们使用流行的“液体模拟优化势”（OPLS）经典力场对分子动力学进行定性再现超临界区域中的此类变化。不幸的是，在160K时，OPLS氮预测的是升华而不是产生液相；因此，我们开发了自己的力场以与实验数据达成定量一致。我们证实了配位数在穿过弗伦克尔线时的渐近行为，并注意到扩散常数的相关变化，这与“转变”从非刚性到刚性的类液体特征一致。这些模拟使我们能够将弗伦克尔线追踪到亚临界温度，并证明它在三相点处终止。这确定了实验上可测量的变化，这些变化可以明确地确定其他系统中的弗伦克尔线。
