Max Planck Institute for Polymer Research , Ackermannweg 10, D-55128 Mainz, Germany.
Center of Smart Interfaces, Technische Universität Darmstadt , Petersenstrasse 32, D-64287 Darmstadt, Germany.
J Chem Theory Comput. 2011 Jun 14;7(6):1916-27. doi: 10.1021/ct2001396. Epub 2011 May 5.
Understanding the relation between structural and thermodynamic quantities obtained with simplified-e.g., coarse-grained (CG) or implicit-solvent-models is an ongoing challenge in the field of multiscale simulation. Assessing the transferability of such models to state points that differ from the one where the model was parametrized is important if one wants to apply these models to complex systems, which, for example, exhibit spatially varying compositions. Here, we investigate the transferability of CG (in this case implicit-solvent) ion models with effective pair potentials derived at very low concentrations to different ion concentrations in aqueous solution. We evaluate both thermodynamic and structural properties of systems of NaCl in aqueous solution both in atomistic explicit-solvent and CG simulations. For the explicit solvent simulations, osmotic coefficients have been calculated at a wide range of salt concentrations and agree very well with experimental data. It had been shown previously that a concentration-dependent dielectric permittivity can be used to make effective implicit-solvent pair potentials transferable since it accounts for the effect of ion concentration on solvent properties, resulting in very good osmotic properties of these models for a certain range of salt concentrations. We investigate the explicit and implicit solvent models also in terms of structural properties, where we can show how with a concentration-dependent dielectric constant one obtains very good structural agreement at low and intermediate salt concentrations, while for larger salt concentrations, multibody ion-ion correlations put a limit to straightforward transferability. We show how-guided by this structural analysis-the transferability of the implicit-solvent model can be improved for high ion concentrations. Doing so, we obtain transferable implicit-solvent effective pair potentials which are both structurally and thermodynamically consistent with an explicit solvent reference model.
理解通过简化模型（例如粗粒化（CG）或隐溶剂模型）获得的结构和热力学量之间的关系是多尺度模拟领域的一个持续挑战。如果要将这些模型应用于具有空间变化组成的复杂系统，那么评估这些模型在与模型参数化的状态点不同的状态点的可转移性非常重要。在这里，我们研究了在非常低的浓度下用有效对势能推导的 CG（在这种情况下是隐溶剂）离子模型在不同离子浓度的水溶液中的可转移性。我们评估了 NaCl 在水溶液中的原子显式溶剂和 CG 模拟中系统的热力学和结构性质。对于显式溶剂模拟，在很宽的盐浓度范围内计算了渗透压系数，并且与实验数据非常吻合。先前已经表明，可以使用浓度依赖性介电常数使有效隐溶剂对势能可转移，因为它考虑了离子浓度对溶剂性质的影响，从而使这些模型在一定范围内的盐浓度下具有非常好的渗透压性质。我们还根据结构性质研究了显式和隐式溶剂模型，在这些模型中，我们可以展示如何使用浓度依赖性介电常数在低和中等盐浓度下获得非常好的结构一致性，而对于较大的盐浓度，多体离子-离子相关性限制了直接可转移性。我们展示了如何通过这种结构分析来提高高离子浓度下隐溶剂模型的可转移性。通过这样做，我们获得了具有结构和热力学一致性的可转移隐溶剂有效对势能，与显式溶剂参考模型一致。
