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Single trajectory transport coefficients and the energy landscape by molecular dynamics simulations

机译:基于分子动力学模拟的单轨迹输运系数和能量景观

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摘要

The Green-Kubo (GK) method is widely used to calculate the transport coefficients of model liquids by Molecular Dynamics (MD) simulation. A reformulation of GK was proposed by Heyes et al. J. Chem. Phys. 150, 174504 (2019), which expressed the shear viscosity in terms of a probability distribution function (PDF) of "single trajectory (ST) viscosities," called "viscuits." This approach is extended here to the bulk viscosity, thermal conductivity, and diffusion coefficient. The PDFs of the four STs expressed in terms of their standard deviations (calculated separately for the positive and negative sides) are shown by MD to be statistically the same for the Lennard-Jones fluid. This PDF can be represented well by a sum of exponentials and is independent of system size and state point in the equilibrium fluid regime. The PDF is not well reproduced by a stochastic model. The PDF is statistically the same as that derived from the potential energy, u, and other thermodynamic quantities, indicating that the transport coefficients are determined quantitatively by and follow closely the time evolution of the underlying energy landscape. The PDFs of out-of-equilibrium supercooled high density states are quite different from those of the equilibrium states.
机译:Green-Kubo(GK)方法被广泛用于通过分子动力学(MD)模拟计算模型液体的输运系数。Heyes 等人提出了 GK 的重新表述 [J. Chem. Phys. 150, 174504 (2019)],它用“单轨迹 (ST) 粘度”的概率分布函数 (PDF) 表示剪切粘度,称为“粘性”。这种方法在这里扩展到体积粘度、导热系数和扩散系数。MD 显示,以标准差表示的四个 ST 的 PDF(分别计算正侧和负侧)在统计学上是相同的,对于 Lennard-Jones 流体。该 PDF 可以用指数的总和很好地表示,并且与平衡流体状态中的系统大小和状态点无关。随机模型不能很好地再现 PDF。PDF在统计学上与势能、u和其他热力学量得出的PDF相同,表明输运系数是由基础能量景观的时间演变定量决定的,并紧随时间演变。非平衡态过冷高密度态的PDF与平衡态的PDF有很大不同。

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