Theoretical Physics Department, African University of Science and Technology, Km 10 Airport Road, Galadimawa, Abuja, Nigeria.
J Chem Phys. 2013 Jan 14;138(2):024316. doi: 10.1063/1.4773821.
Properties of liquid water have been computed using a near-exact rigid-monomer two-body (pairwise-additive) force field and the same field supplemented by a simple, non-empirical polarization model of pairwise nonadditive many-body forces. The inclusion of nonadditive polarization forces leads to a dramatic decrease, sometimes by an order of magnitude, of the deviations of water properties computed using classical molecular dynamics from experiment results. The remaining deviations are typically of the order of 10%. The model correctly predicts the temperature dependence of the properties except for the density of supercooled water. This good performance is achieved despite the known failure of the polarization model in reproducing trimer nonadditive interaction energies, confirmed here by showing that for a random set of trimers with all O-O separations smaller than 3.4 Å, selected from simulation snapshots, the average error of the model relative to accurate ab initio values is 71%. However, the errors gradually decrease for larger trimers, more abundant in liquid, and one can estimate that the polarization model should reproduce the exact liquid interaction energy to within about 6%. Although this accuracy is consistent with the observed performance of the polarization model, it does not explain the dramatic improvements over the two-body model. These improvements are due to the restructuring of liquid into tetrahedral arrangements instigated by the nonadditive polarization forces. The deviations of our predictions from experiments are generally also consistent with the estimated contributions from leading neglected effects other than the exchange nonadditive forces: the monomer flexibility and quantum nuclear motion effects.
使用近乎精确的刚性单体二体（两两附加）力场和相同的场，辅以简单的非经验极化模型来计算液体水的性质，该模型对非附加多体力进行两两补充。包含非附加极化力会导致使用经典分子动力学计算的水性质与实验结果的偏差急剧下降，有时下降一个数量级。剩余的偏差通常在 10%左右。该模型正确预测了性质随温度的变化，除了过冷水的密度。尽管众所周知极化模型在再现三聚体非附加相互作用能方面存在失败，这里通过表明从模拟快照中选择的所有 O-O 间距小于 3.4 Å 的随机三聚体，模型相对于准确从头算值的平均误差为 71%，但该模型仍能实现良好的性能，从而证实了这一点。然而，对于更大的三聚体，其误差逐渐减小，而且在液体中更为丰富，因此可以估计极化模型应该能够将精确的液体相互作用能再现到约 6%以内。尽管这种精度与极化模型的观察性能一致，但它并不能解释与二体模型相比的显著改进。这些改进归因于非附加极化力引发的液体向四面体排列的重构。我们的预测与实验的偏差也与除交换非附加力之外的主要被忽略效应的估计贡献一致：单体灵活性和量子核运动效应。
