Wu Yujie, Tepper Harald L, Voth Gregory A
Center for Biophysical Modeling and Simulation and Department of Chemistry, University of Utah, 315 South 1400 East Room 2020, Salt Lake City, Utah 84112-0850, USA.
J Chem Phys. 2006 Jan 14;124(2):024503. doi: 10.1063/1.2136877.
In order to introduce flexibility into the simple point-charge (SPC) water model, the impact of the intramolecular degrees of freedom on liquid properties was systematically studied in this work as a function of many possible parameter sets. It was found that the diffusion constant is extremely sensitive to the equilibrium bond length and that this effect is mainly due to the strength of intermolecular hydrogen bonds. The static dielectric constant was found to be very sensitive to the equilibrium bond angle via the distribution of intermolecular angles in the liquid: A larger bond angle will increase the angle formed by two molecular dipoles, which is particularly significant for the first solvation shell. This result is in agreement with the work of Hochtl et al. [J. Chem. Phys. 109, 4927 (1998)]. A new flexible simple point-charge water model was derived by optimizing bulk diffusion and dielectric constants to the experimental values via the equilibrium bond length and angle. Due to the large sensitivities, the parametrization only slightly perturbs the molecular geometry of the base SPC model. Extensive comparisons of thermodynamic, structural, and kinetic properties indicate that the new model is much improved over the standard SPC model and its overall performance is comparable to or even better than the extended SPC model.
为了给简单点电荷（SPC）水模型引入灵活性，本工作系统研究了分子内自由度对液体性质的影响，并将其作为多种可能参数集的函数。研究发现，扩散常数对平衡键长极为敏感，且这种影响主要源于分子间氢键的强度。通过液体中分子间角度的分布，发现静态介电常数对平衡键角非常敏感：较大的键角会增大两个分子偶极形成的角度，这对第一溶剂化层尤为重要。该结果与霍赫特尔等人的工作[《化学物理杂志》109, 4927 (1998)]一致。通过经由平衡键长和键角将体扩散和介电常数优化至实验值，推导出了一种新的灵活简单点电荷水模型。由于敏感性较高，参数化仅对基础SPC模型的分子几何结构产生轻微扰动。对热力学、结构和动力学性质的广泛比较表明，新模型相比标准SPC模型有很大改进，其整体性能与扩展SPC模型相当甚至更好。
