表征纯CH4，CF4和CH4 / CF4混合物的多尺度方法,The Journal of Chemical Physics

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表征纯CH4，CF4和CH4 / CF4混合物的多尺度方法
The Journal of Chemical Physics ( IF 3.1 ) Pub Date : 2015-04-28 13:55:51 , DOI: 10.1063/1.4919079
Joyjit Chattoraj ₁ , Tobias Risthaus _{2,

3} , Oliver Rubner ₁ , Andreas Heuer ₁ , Stefan Grimme ₂

Affiliation

在这项研究中，我们使用一种新的 从头算 方法开发了甲烷（CH ₄），四氟甲烷（CF ₄）和CH ₄ / CF ₄二聚体的三种分子间电位。最终目标是从微观上了解CH ₄ / CF ₄系统中的相分离，该相分离发生在接近其凝固点的液态中。使用 从头算起进行纯CH ₄系统的蒙特卡洛（MC）模拟能量来验证潜力。该模拟很好地再现了实验已知的液体密度，内部能量，第二维里系数和径向分布函数。然后，使用反向蒙特卡洛技术将基本为6维（6D）的从头电势降低为一维（1D）有效电势。这种潜力也成功地再现了实验结果。有趣的是，MC研究不能扩展到纯CF ₄系统和CH ₄ / CF ₄混合系统，因为这两个 从头开始 势代表非常粗糙的势态。这使得MC模拟的能量插值不可靠，因此多尺度方法不可靠。然而，这暗示了在低温下通过实验观察到的CH ₄ / CF ₄体系相分离的可能驱动力。此外，我们仔细研究了通过逆MC技术确定一维有效电位的方法。我们认为，对于一个很好的近似值，一维电势的温度依赖性可以通过针对固定温度的加权技术来估计。

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A multi-scale approach to characterize pure CH4, CF4, and CH4/CF4 mixtures

In this study, we develop three intermolecular potentials for methane (CH₄), tetrafluoromethane (CF₄), and CH₄/CF₄ dimers using a novel ab initio method. The ultimate goal is to understand microscopically the phase-separation in CH₄/CF₄ systems, which takes place in the liquid states near their freezing points. Monte-Carlo (MC) simulations of the pure CH₄ system are performed using the ab initio energies to verify the potential. The simulations reproduce quite well the experimentally known liquid densities, the internal energies, the second virial coefficients, and the radial distribution function. The essentially six-dimensional (6D) ab initio potential is then reduced to a one-dimensional (1D) effective potential using the inverse Monte-Carlo technique. This potential, too, successfully reproduces the experimental results. Interestingly, the MC study cannot be extended to the pure CF₄ system and the CH₄/CF₄ mixed system because the two respective ab initio potentials present very rough potential landscapes. This renders the interpolation of energies for the MC simulations and thus the multi-scale approach unreliable. It suggests, however, a possible driving force for the experimentally observed phase separation of the CH₄/CF₄ system at low temperatures. Furthermore, we carefully study the determination of 1D effective potentials via inverse MC techniques. We argue that to a good approximation the temperature dependence of the 1D potentials can be estimated via reweighting techniques for a fixed temperature.

更新日期：2015-04-29

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