Fick diffusion coefficients of liquid mixtures directly obtained from equilibrium molecular dynamics.
Fick diffusion coefficients of liquid mixtures directly obtained from equilibrium molecular dynamics.
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DOI：
10.1021/jp208360s
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发表时间：
2011-10
期刊：
影响因子：
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通讯作者：
Xin Liu;S. K. Schnell;J. Simon;D. Bedeaux;S. Kjelstrup;A. Bardow;T. Vlugt
中科院分区：
文献类型：
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作者：
Xin Liu;S. K. Schnell;J. Simon;D. Bedeaux;S. Kjelstrup;A. Bardow;T. Vlugt
提出了一种直接从平衡分子动力学（MD）模拟计算Fick扩散系数的方法，并对丙酮-甲醇和丙酮-四氯化碳液体混合物进行了验证。Fick扩散系数由Maxwell-Stefan（MS）扩散系数和所谓的热力学因子获得。MS扩散系数描述了不同组分之间的摩擦，而热力学因子是活性的浓度导数，描述了与理想混合行为的偏差。重要的是要注意，所有的相互扩散实验测量菲克扩散系数，而分子模拟提供MS扩散系数。所需的热力学因子转换MS到菲克扩散系数，反之亦然，但是，通常很难提取模拟和实验之间的理论和应用的差距。在这里，我们采用我们的新方法来计算平衡MD模拟中小尺度密度波动的热力学因子[Chem.Phys.Lett.2011，504，199-201]。以前，该方法仅针对具有单个相互作用位点的分子开发和验证。在这项工作中，我们将这种方法应用于丙酮-甲醇和丙酮-四氯化碳液体混合物，并表明该方法在这些更复杂的系统中也能很好地工作。这提供了直接从平衡MD模拟中提取Fick扩散系数的缺失步骤。丙酮-甲醇和丙酮-四氯化碳混合物的Fick扩散系数的计算值与实验值吻合得很好。因此，建议的框架提供了一个有效的途径来模拟液体中的扩散的基础上，一个一致的分子图片。
A methodology for computing Fick diffusivities directly from equilibrium molecular dynamics (MD) simulations is presented and validated for acetone-methanol and acetone-tetrachloromethane liquid mixtures. Fick diffusivities are obtained from Maxwell-Stefan (MS) diffusivities and the so-called thermodynamic factor. MS diffusivities describe the friction between different components, while the thermodynamic factor is the concentration derivative of the activity describing the deviation from ideal mixing behavior. It is important to note that all mutual diffusion experiments measure Fick diffusion coefficients, while molecular simulation provides MS diffusivities. The required thermodynamic factor to convert MS into Fick diffusivities and vice versa, however, is usually difficult to extract from both simulations and experiments leaving a gap between theory and application. Here, we employ our novel method to compute the thermodynamic factor from small-scale density fluctuations in equilibrium MD simulations [Chem. Phys. Lett.2011, 504, 199-201]. Previously, this method was developed and validated for molecules with single interaction sites only. In this work, we applied this method to acetone-methanol and acetone-tetrachloromethane liquid mixtures and show that the method also works well in these more complex systems. This provides the missing step to extract Fick diffusion coefficients directly from equilibrium MD simulations. The computed Fick diffusivities of acetone-methanol and acetone-tetrachloromethane mixtures are in excellent agreement with experimental values. The suggested framework thus provides an efficient route to model diffusion in liquids on the basis of a consistent molecular picture.