Faculty of Science, University of Split, Rudjera Boškovića 33, Split 21000, Croatia.
Fakultät Physik/DELTA, Technische Universität Dortmund, Dortmund D-44221, Germany.
J Phys Chem B. 2020 Sep 24;124(38):8358-8371. doi: 10.1021/acs.jpcb.0c05932. Epub 2020 Sep 14.
The X-ray scattering intensities (()) of linear alkanols OH(CH)CH obtained from experiments (methanol to 1-undecanol) and computer simulations (methanol to 1-nonanol) of different force field models are comparatively studied particularly in order to explain the origin and the properties of the scattering pre-peak in the -vector range 0.3-1 Å. The experimental () values show two apparent features: the pre-peak position decreases with increasing , and more intriguingly, the amplitude goes through a maximum at 1-butanol ( = 4). The first feature is well reproduced by all force-field models, while the second shows strong model dependence. The simulations reveal various shapes of clusters of the hydroxyl head-group from >2. is directly related to the size of the meta-objects corresponding to such clusters surrounded by their alkyl tails. The explanation of the turnover at = 4 is more involved in terms of cancellations of atom-atom structure factor () contributions related to domain ordering. The flexibility of the alkyl tails tends to reduce the cross contributions, thus revealing the crucial importance of this parameter in the models. Force fields with all-atom representation are less successful in reproducing the pre-peak features for smaller alkanols, <6, possibly because they blur the charge ordering process since all atoms bear partial charges. The analysis clearly shows that it is not possible to obtain a model-free explanation of the features of ().
我们对比研究了不同力场模型的实验（甲醇至 1-十一醇）和计算机模拟（甲醇至 1-壬醇）得到的线性伯醇 OH(CH)CH 的 X 射线散射强度（()），目的是解释散射前峰在 0.3-1 Å-1 范围内的起源和性质。实验（()）值表现出两个明显的特征：前峰位置 随着 的增加而减小，更有趣的是，幅度 在 1-丁醇（ = 4）处出现最大值。所有力场模型都很好地再现了第一个特征，而第二个特征则表现出强烈的模型依赖性。模拟揭示了羟基头基团的各种形状的团簇，从 >2. 直接与对应于这些团簇的超结构的大小相关，这些超结构被其烷基尾包围。 = 4 处的 翻转的解释涉及到与域序有关的原子-原子结构因子（）贡献的抵消。烷基尾的灵活性倾向于减少交叉贡献，因此表明该参数在模型中的重要性。具有全原子表示的力场在较小的伯醇（<6）中再现前峰特征的效果较差，可能是因为它们模糊了电荷有序过程，因为所有原子都带有部分电荷。分析清楚地表明，不可能对（）的特征进行无模型解释。
