论文标题

通过平衡分子动力学模拟的受限流体的采样迁移率

Sampling mobility profiles of confined fluids with equilibrium molecular dynamics simulations

论文作者

Mangaud, Etienne, Rotenberg, Benjamin

论文摘要

我们展示了如何评估迁移率,表征了在扰动下从平衡分子模拟中的受lip液的转运。与绿色kubo形式主义得出的相关功能很难准确地采样,我们考虑了两种互补策略:由于对当地磁通的新估计值的新估计值,涉及在粒子上作用于粒子的力量和速度,并改善了临时抽样的局部力量,因此改善了空间抽样,并改善了einstein-Helfo,而不是Green-Helfo erne green-kkub and green-kub and green-kkub and green-kkub and green-kkub and green-kkub and-kkub and-kkub and the Green-kkub。我们在压力或化学势梯度下限制在平行壁之间的二元混合物的情况下说明了这种方法。将所有平衡方法与标准的非平衡分子动力学(NEMD)进行比较,并提供正确的迁移率。我们在孔的大部分部分中恢复定量流体粘度和最大的迁移率。有趣的是,与总通量的Onsager矩阵不同,局部通量的迁移率矩阵不是对称的。即使是计算上最有效的平衡方法(爱因斯坦 - 赫尔凡德与基于力的估计器相结合)也比确定单个迁移率曲线的效率较低。但是,平衡方法同时提供了对所有扰动的所有响应,而NEMD需要模拟几种类型的扰动来确定各种响应,每个响应都具有不同的幅度,以检查线性制度的有效性。尽管NEMD在本例中似乎更具竞争力,但对于更复杂的系统,平衡应该不同,特别是对于电解质解决方案,以应对压力,盐浓度和电势梯度的响应。

We show how to evaluate mobility profiles, characterizing the transport of confined fluids under a perturbation, from equilibrium molecular simulations. The correlation functions derived with the Green-Kubo formalism are difficult to sample accurately and we consider two complementary strategies: improving the spacial sampling thanks to a new estimator of the local fluxes involving the forces acting on the particles in addition to their positions and velocities, and improving temporal sampling thanks to the Einstein-Helfand approach instead of the Green-Kubo one. We illustrate this method on the case of a binary mixture confined between parallel walls, under a pressure or chemical potential gradient. All equilibrium methods are compared to standard non-equilibrium molecular dynamics (NEMD) and provide the correct mobility profiles. We recover quantitatively fluid viscosity and diffusio-osmostic mobility in the bulk part of the pore. Interestingly, the matrix of mobility profiles for local fluxes is not symmetric, unlike the Onsager matrix for the total fluxes. Even the most computationally efficient equilibrium method (Einstein-Helfand combined with the force-based estimator) remains less efficient than NEMD to determine a single mobility profile. However, the equilibrium approach provides all responses to all perturbations simultaneously, whereas NEMD requires the simulation of several types of perturbations to determine the various responses, each with different magnitudes to check the validity of the linear regime. While NEMD seems more competitive for the present example, the balance should be different for more complex systems, in particular for electrolyte solutions for the responses to pressure, salt concentration and electric potential gradients.

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