Force Field Parametrization from the Hirshfeld Molecular Electronic Density

The Hirshfeld charges are linearly increased to reproduce the experimental dielectric constant of 10 polar solvents having values between 13 (pyridine) and 182 (N-methylformamide). The OPLS/AA force field is used to obtain the new parameters. The surface tension and liquid density are also target properties to determine the new nonbonding parameters. The charge scaling factor is between 1.2 and 1.3. In addition, properties that were not used in the parametrization procedure, such as the heat of vaporization, self-diffusion coefficient, shear viscosity, isothermal compressibility, and volumetric expansion coefficient are obtained. Binary mixtures of amide/water and amide/amide are also studied. The original parameters of OPLS/AA, CGenFF, and GAFF force fields are evaluated. The TIP4P/ε force field is used to simulate water. The results from this work with the new parameters, for both pure components and binary mixtures, are in better agreement with experimental data than those obtained with the original values for most of the calculated properties. The maximum density of N-methylformamide in aqueous solutions is correctly predicted only with the new parameters. The high value of the dielectric constant of acetamide, formamide, and N-methylformamide is discussed in terms of the chain formation from the hydrogen bond interactions.

为复现10种极性溶剂的实验介电常数（取值范围为13（吡啶）至182（N-甲基甲酰胺）），我们对赫尔希菲尔德电荷（Hirshfeld charges）进行线性调整。本研究采用OPLS/AA力场（OPLS/AA force field）以推导全新的力场参数，同时将表面张力与液体密度作为目标优化属性，以确定新的非键相互作用参数。电荷缩放因子的取值区间为1.2至1.3。除此之外，本研究还计算了参数化过程中未被纳入拟合的物性，包括汽化热、自扩散系数、剪切粘度、等温压缩率与体积膨胀系数。同时对酰胺/水及酰胺/酰胺二元混合体系展开了研究，并对OPLS/AA、CGenFF与GAFF三款原始力场的参数进行了性能评估。模拟水相体系时，采用TIP4P/ε力场（TIP4P/ε force field）。相较于采用原始力场参数得到的计算结果，本研究基于新参数得到的纯组分与二元混合体系的物性结果，在绝大多数计算物性上与实验数据的吻合度更优。仅通过本研究提出的新参数，方能准确预测水溶液中N-甲基甲酰胺的最大密度。最后，针对乙酰胺、甲酰胺与N-甲基甲酰胺的高介电常数特性，本文从氢键相互作用引发的链状结构形成角度进行了讨论。