Patel Sandeep, Brooks Charles L
Department of Molecular Biology (TPC-6), The Scripps Research Institute, La Jolla, California 92037, USA.
J Chem Phys. 2005 Jan 8;122(2):024508. doi: 10.1063/1.1827604.
We study the bulk and interfacial properties of methanol via molecular dynamics simulations using a CHARMM (Chemistry at HARvard Molecular Mechanics) fluctuating charge force field. We discuss the parametrization of the electrostatic model as part of the ongoing CHARMM development for polarizable protein force fields. The bulk liquid properties are in agreement with available experimental data and competitive with existing fixed-charge and polarizable force fields. The liquid density and vaporization enthalpy are determined to be 0.809 g/cm3 and 8.9 kcal/mol compared to the experimental values of 0.787 g/cm3 and 8.94 kcal/mol, respectively. The liquid structure as indicated by radial distribution functions is in keeping with the most recent neutron diffraction results; the force field shows a slightly more ordered liquid, necessarily arising from the enhanced condensed phase electrostatics (as evidenced by an induced liquid phase dipole moment of 0.7 D), although the average coordination with two neighboring molecules is consistent with the experimental diffraction study as well as with recent density functional molecular dynamics calculations. The predicted surface tension of 19.66+/-1.03 dyn/cm is slightly lower than the experimental value of 22.6 dyn/cm, but still competitive with classical force fields. The interface demonstrates the preferential molecular orientation of molecules as observed via nonlinear optical spectroscopic methods. Finally, via canonical molecular dynamics simulations, we assess the model's ability to reproduce the vapor-liquid equilibrium from 298 to 423 K, the simulation data then used to obtain estimates of the model's critical temperature and density. The model predicts a critical temperature of 470.1 K and critical density of 0.312 g/cm3 compared to the experimental values of 512.65 K and 0.279 g/cm3, respectively. The model underestimates the critical temperature by 8% and overestimates the critical density by 10%, and in this sense is roughly equivalent to the underlying fixed-charge CHARMM22 force field.
我们通过使用CHARMM（哈佛分子力学中的化学）波动电荷力场的分子动力学模拟来研究甲醇的体相和界面性质。我们讨论了静电模型的参数化，这是正在进行的用于可极化蛋白质力场的CHARMM开发的一部分。体相液体性质与现有实验数据一致，并且与现有的固定电荷和可极化力场具有竞争力。液体密度和汽化焓分别确定为0.809 g/cm³和8.9 kcal/mol，而实验值分别为0.787 g/cm³和8.94 kcal/mol。径向分布函数表明的液体结构与最新的中子衍射结果一致；力场显示出稍微更有序的液体，这必然源于增强的凝聚相静电作用（液相诱导偶极矩为0.7 D证明了这一点），尽管与两个相邻分子的平均配位与实验衍射研究以及最近的密度泛函分子动力学计算一致。预测的表面张力为19.66±1.03 dyn/cm，略低于实验值22.6 dyn/cm，但仍与经典力场具有竞争力。界面展示了通过非线性光学光谱方法观察到的分子的优先分子取向。最后，通过正则分子动力学模拟，我们评估了该模型从298到423 K再现气液平衡的能力，模拟数据随后用于获得该模型的临界温度和密度的估计值。该模型预测的临界温度为470.1 K，临界密度为0.312 g/cm³，而实验值分别为512.65 K和0.279 g/cm³。该模型将临界温度低估了8%，将临界密度高估了10%，从这个意义上说，它大致相当于基础的固定电荷CHARMM22力场。
