IFP Energies Nouvelles, 1 et 4 avenue de Bois-Préau, 92852 Rueil-Malmaison, France.
J Phys Chem B. 2013 Jun 13;117(23):7123-32. doi: 10.1021/jp401251w. Epub 2013 Jun 3.
In this work, a new transferable united-atom force field has been developed to predict phase equilibrium and hydration free energy of carboxylic acids. To take advantage of the transferability of the AUA4 force field, all Lennard-Jones parameters of groups involved in the carboxylic acid chemical function are reused from previous parametrizations of this force field. Only a unique set of partial electrostatic charges is proposed to reproduce the experimental gas phase dipole moment, saturated liquid densities and vapor pressures. Phase equilibrium properties of various pure carboxylic acids (acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid) and one diacid (1,5-pentanedioic) are studied through Monte Carlo simulations in the Gibbs ensemble. A good accuracy is obtained for pure compound saturated liquid densities and vapor pressures (average deviation of 2% and 6%, respectively), as well as for critical points. The vaporization enthalpy is, however, poorly predicted for short acids, probably due to a limitation of the force field to correctly describe the significant dimerization in the vapor phase. Pressure-composition diagrams for two binary mixtures (acetic acid + n-butane and propanoic acid + pentanoic acid) are also computed with a good accuracy, showing the transferability of the proposed force field to mixtures. Hydration free energies are calculated for three carboxylic acids using thermodynamic integration. A systematic overestimation of around 10 kJ/mol is observed compared to experimental data. This new force field parametrized only on saturated equilibrium properties appears insufficient to reach an acceptable precision for this property, and only relative hydration free energies between two carboxylic acids can be correctly predicted. This highlights the limitation of the transferability feature of force fields to properties not included in the parametrization database.
在这项工作中，开发了一种新的可转移的统一原子力场，以预测羧酸的相平衡和水合自由能。为了利用 AUA4 力场的可转移性，涉及羧酸化学功能的所有 Lennard-Jones 参数都从该力场以前的参数化中重复使用。仅提出了一组独特的部分静电电荷，以重现实验气相偶极矩、饱和液体密度和蒸气压。通过 Gibbs 系综中的蒙特卡罗模拟研究了各种纯羧酸（乙酸、丙酸、丁酸、戊酸、己酸）和一种二酸（1,5-戊二酸）的相平衡性质。对于纯化合物饱和液体密度和蒸气压（平均偏差分别为 2%和 6%）以及临界点，获得了很好的精度。然而，对于短链酸，汽化焓的预测精度较差，这可能是由于力场无法正确描述气相中显著的二聚化。还使用该力场计算了两个二元混合物（乙酸+正丁烷和丙酸+戊酸）的压力-组成图，精度也很高，表明该力场对混合物具有可转移性。使用热力学积分法计算了三种羧酸的水合自由能。与实验数据相比，观察到约 10 kJ/mol 的系统高估。与仅基于饱和平衡性质参数化的这个新力场相比，对于这个性质，它的精度仍然不够，只能正确预测两个羧酸之间的相对水合自由能。这突出了力场的可转移性特征在不包括在参数化数据库中的性质上的局限性。
