Aina Alex A, Misquitta Alston J, Price Sarah L
Department of Chemistry, University College London, 20 Gordon St., London WC1H 0AJ, United Kingdom.
School of Physics and Astronomy and The Thomas Young Centre for Theory and Simulation of Materials at Queen Mary, University of London, London E1 4NS, United Kingdom.
J Chem Phys. 2021 Mar 7;154(9):094123. doi: 10.1063/5.0043746.
An anisotropic atom-atom distributed intermolecular force-field (DIFF) for rigid trinitrobenzene (TNB) is developed using distributed multipole moments, dipolar polarizabilities, and dispersion coefficients derived from the charge density of the isolated molecule. The short-range parameters of the force-field are fitted to first- and second-order symmetry-adapted perturbation theory dimer interaction energy calculations using the distributed density-overlap model to guide the parameterization of the short-range anisotropy. The second-order calculations are used for fitting the damping coefficients of the long-range dispersion and polarization and also for relaxing the isotropic short-range coefficients in the final model, DIFF-srL2(rel). We assess the accuracy of the unrelaxed model, DIFF-srL2(norel), and its equivalent without short-range anisotropy, DIFF-srL0(norel), as these models are easier to derive. The model potentials are contrasted with empirical models for the repulsion-dispersion fitted to organic crystal structures with multipoles of iterated stockholder atoms (ISAs), FIT(ISA,L4), and with Gaussian Distributed Analysis (GDMA) multipoles, FIT(GDMA,L4), commonly used in modeling organic crystals. The potentials are tested for their ability to model the solid state of TNB. The non-empirical models provide more reasonable relative lattice energies of the three polymorphs of TNB and propose more sensible hypothetical structures than the empirical force-field (FIT). The DIFF-srL2(rel) model successfully has the most stable structure as one of the many structures that match the coordination sphere of form III. The neglect of the conformational flexibility of the nitro-groups is a significant approximation. This methodology provides a step toward force-fields capable of representing all phases of a molecule in molecular dynamics simulations.
利用从孤立分子的电荷密度导出的分布多极矩、偶极极化率和色散系数，开发了一种用于刚性三硝基苯（TNB）的各向异性原子-原子分布式分子间力场（DIFF）。力场的短程参数通过使用分布密度重叠模型拟合到一阶和二阶对称适应微扰理论二聚体相互作用能计算中，以指导短程各向异性的参数化。二阶计算用于拟合长程色散和极化的阻尼系数，也用于在最终模型DIFF-srL2(rel)中放宽各向同性短程系数。我们评估了未放宽模型DIFF-srL2(norel)及其无短程各向异性的等效模型DIFF-srL0(norel)的准确性，因为这些模型更容易推导。将模型势与用于拟合具有迭代股东原子（ISA）多极的有机晶体结构的排斥-色散经验模型FIT(ISA,L4)以及常用于有机晶体建模的高斯分布分析（GDMA）多极FIT(GDMA,L4)进行对比。测试了这些势对TNB固态建模的能力。非经验模型提供了比经验力场（FIT）更合理的TNB三种多晶型的相对晶格能，并提出了更合理的假设结构。DIFF-srL2(rel)模型成功地将最稳定的结构作为与晶型III配位球匹配的众多结构之一。忽略硝基的构象灵活性是一个重大近似。这种方法为能够在分子动力学模拟中表示分子所有相的力场迈出了一步。
