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.

中文翻译：

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从二聚体到固态：吡啶的分子间力场

使用吡啶原子的各向异性原子-原子力场，利用分布的原子多极子，极化率和色散系数，以及从对称自适应扰动理论（密度泛函理论）二聚体计算得出的各向异性原子-原子排斥模型，对吡啶晶体进行建模结构。在这里，我们表明，这种分布的分子间力场（DIFF）可以像对除静电项以外的所有其他项建模一样准确地对实验晶体结构进行建模，而静电项具有各向同性排斥-分散电势，该电势已经适合于实验晶体结构。在这两种情况下，这种差异都可与晶体结构随温度，压力或零点振动效应的忽略而发生的变化相媲美。进行了晶体结构预测研究，并且观察到的多晶型与假设的热力学竞争晶体结构形成对比。DIFF模型能够确定未报告的吡啶高压相的结构，这与经验拟合势不同。因此，DIFF模型方法提供了一个潜在的成对的势能表面模型，我们已经成功地转移到了结晶相，尽管对多体项的处理需要改进，并且成对的势能有些过度结合。此外，对具有同位素多态性的系统的研究突出表明，使用经验势能部分吸收了温度和零点运动效应，以及在功能形式中未明确表示的分子间力。