Self-Consistent Scheme Combining MD and Order-N DFT Methods: An Improved Set of Nonpolarizable Force Fields for Ionic Liquids
Self-Consistent Scheme Combining MD and Order-N DFT Methods: An Improved Set of Nonpolarizable Force Fields for Ionic Liquids
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DOI：
10.1021/acs.jctc.9b00793
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发表时间：
2020-01-01
影响因子：
5.5
通讯作者：
Matubayasi, Nobuyuki
中科院分区：
文献类型：
--
作者：
Ishii, Yoshiki;Matubayasi, Nobuyuki
采用基于N阶密度泛函理论（DFT）的分子动力学（MD）模拟和第一性原理计算的自洽方案，对离子液体的非极化力场进行了调谐.用整个MD盒进行DFT计算，确定了原子电荷，有效地解释了电荷转移和分子内极化的多体效应。这些电荷代表了凝聚相在不可极化力场框架内的有效相互作用，并且可以作为一个明确的多体模型的替代方案，例如，极化率。在这里，我们展示了性能的非极化力场确定的MD-DFT自洽方案在咪唑，吡咯烷和铵基离子液体。分子电荷随离子液体组成的变化范围比随热力学条件的变化范围大得多，电荷有序结构随有效电荷的增加而系统性减弱。对于能量性质，虽然计算的蒸发热取决于原子和分子电荷，但相应的热容不会受到基于DFT的变化的强烈影响。对于输运性质，自扩散系数，电导率和粘度变化更大的自洽方案。DFT有效电荷的引入增强了离子液体的流动性，提高了电导率和粘度的准确性。这是由于离子之间的相互作用减弱，并且通过MD和DFT的迭代很好地校正了用全电荷模型观察到的太慢的运动。因此，我们得出结论，一组非极化力场与MD-DFT自洽方案得到的离子液体的输运性质的更好的描述。
The nonpolarizable force field of ionic liquids is tuned by using the self-consistent scheme of molecular dynamics (MD) simulation and first-principles calculation based on the order-N density functional theory (DFT). The atomic charges are determined by using the whole MD cell for DFT calculation and accounts effectively for the many-body effects of charge transfer and intramolecular polarization. The charges represent effective interactions in the condensed phase within the framework of the nonpolarizable force field and can be an alternative for an explicitly many-body model incorporating, for example, polarizability. Here we demonstrate the performance of nonpolarizable force field determined with the MD-DFT self-consistent scheme in imidazolium-, pyrrolidinium-, and ammonium-based ionic liquids. The variation ranges of molecular charges are much larger with the compositions of the ionic liquid than with the thermodynamic conditions, and the charge-ordering structures become systematically weaker with the effective charges. For energetic properties, while the calculated heat of vaporization depends on the atomic and molecular charges, the corresponding heat capacity is not strongly affected by the DFT-based variation. For transport properties, the self-diffusion coefficient, electrical conductivity, and viscosity vary much more in the self-consistent scheme. The effective DFT charge is observed to enhance the fluidity of ionic liquids and improve the accuracy of electrical conductivity and viscosity. This is due to the weakened interactions among the ions, and the too slow motions observed with a full-charge model are well corrected through the iteration of MD and DFT. We therefore conclude that the set of nonpolarizable force fields obtained with the MD-DFT self-consistent scheme leads to better description of transport properties of ionic liquids.