For an MD system representing a monatomic liquid, the distribution of $3N$-dimensional potential energy structures consists of two classes, random and symmetric. This distribution is shown and discussed for liquid Na. The random class constitutes the liquid phase domain. In V-T theory, the liquid atomic motion consists of prescribed vibrations in a random valley, plus parameterized transit motions between valleys. The theory has been strongly verified at 395.1K, a bit above melting. Our goal here is to test this theory for its ability to explain the temperature ($T$) dependence of the mean square displacement (MSD) at $T\leq395.1$K. The test results are positive at 204.6K, where the time evolution equations, controlled by a transit rate decreasing with $T$, accurately account for MD data for the MSD. To test at significantly lower $T$, where the MD system does not remain in the liquid phase, the theoretical liquid MSD is calibrated for $T\leq$ 204.6K. The Kob-Andersen (K-A) dynamic slowing down graph is shown for liquid Na at $T\leq395.1$K. The following observations are discussed in terms of the atomic motion. (a) The agreement between pure vibrational motion and MD data for time correlation functions in the vibrational interval is so far highly accurate. (b) The "bump" ahead of the plateau in the MSD at low $T$ is attributed to the vibrational excess. (c) The K-A graph from theory for liquid Na, and the same graphs from MD data for a liquid Lennard-Jones binary mixture (BMLJ) and liquid silica, are identical in the ballistic period and in the purely diffusive time interval. (d) The glass transition proceeds in the symmetric manifold. These and other discussions confirm that V-T theory can explain the $T$ dependence observed in K-A graphs.
Local collective dynamics at equilibrium BCC crystal-melt interfaces
我们提出了一个经典的分子动力学研究的集体动力学性质的共存液相平衡体心立方（BCC）铁晶体-熔体界面。对于三个界面取向（100），（110）和（111），集体动力学的特征在于通过计算的中间散射函数，动力学结构因子和密度弛豫时间在一个连续的局部区域的兴趣。在所有三个BCC晶体-熔体界面取向的集体动力学的各向异性加速观察。这一趋势与先前观察到的液-气界面局部集体动力学的减缓明显不同[Acta Mater 2020;198：281]。通过研究界面密度弛豫时间，我们重新审视了最近发展的凝固晶体-熔体界面动力学系数的时间相关的Ginzburg-Landau（TDGL）理论的有效性，结果与非平衡MD模拟测量的CMI动力学系数的大小和动力学各向异性非常一致
