Department of Chemistry, University College London, London WC1H 0AJ, United Kingdom.
School of Physics and Astronomy, Queen Mary, University of London, London E1 4NS, United Kingdom.
J Chem Phys. 2017 Oct 28;147(16):161722. doi: 10.1063/1.4999789.
An anisotropic atom-atom force-field for pyridine, using distributed atomic multipoles, polarizabilities, and dispersion coefficients and an anisotropic atom-atom repulsion model derived from symmetry-adapted perturbation theory (density functional theory) dimer calculations, is used to model pyridine crystal structures. Here we show that this distributed intermolecular force-field (DIFF) models the experimental crystal structures as accurately as modelling all but the electrostatic term with an isotropic repulsion-dispersion potential that has been fitted to experimental crystal structures. In both cases, the differences are comparable to the changes in the crystal structure with temperature, pressure, or neglect of zero-point vibrational effects. A crystal structure prediction study has been carried out, and the observed polymorphs contrasted with hypothetical thermodynamically competitive crystal structures. The DIFF model was able to identify the structure of an unreported high pressure phase of pyridine, unlike the empirically fitted potential. The DIFF model approach therefore provides a model of the underlying pair potential energy surface that we have transferred to the crystalline phase with a considerable degree of success, though the treatment of the many-body terms needs improvement and the pair potential is slightly over-binding. Furthermore, this study of a system that exhibits isotopic polymorphism highlights that the use of an empirical potential has partially absorbed temperature and zero-point motion effects as well as the intermolecular forces not explicitly represented in the functional form. This study therefore highlights the complexity in modelling crystallization phenomena from a realistic pair potential energy surface.
采用分布式原子多极矩、极化率和色散系数以及源自对称自适应微扰理论（密度泛函理论）二聚体计算的各向异性原子-原子排斥模型，为吡啶构建各向异性原子-原子力场，以模拟吡啶晶体结构。我们发现，与使用拟合实验晶体结构的各向同性排斥-色散势仅拟合静电项的模型相比，该分布式分子间力场（DIFF）能够更准确地模拟实验晶体结构。在这两种情况下，差异与晶体结构随温度、压力或忽略零点振动效应的变化相当。我们进行了晶体结构预测研究，并将观察到的多晶型物与假设的热力学竞争晶体结构进行了对比。DIFF 模型能够识别未报道的吡啶高压相的结构，而经验拟合势则不能。因此，DIFF 模型方法提供了一个潜在的对势能表面模型，我们已经成功地将其转移到晶体相，尽管需要改进多体项的处理，并且对势能的拟合稍微过强。此外，这项对表现出同位素多晶型的系统的研究强调，使用经验势部分吸收了温度和零点运动效应以及功能形式中未明确表示的分子间力。因此，这项研究突出了从实际对势能表面建模结晶现象的复杂性。
