A revolution in resolution is occurring now in electron microscopy arising from the development of methods for imaging single particles at cryogenic temperatures and obtaining electron diffraction data from nanocrystals of small organic molecules or macromolecules. Near-atomic or even atomic resolution of molecular structures can be achieved. The basis of these methods is the scattering of an electron beam due to the electrostatic potential of the sample. To analyse these high-quality experimental data, it is necessary to use appropriate atomic scattering factors. The independent atom model (IAM) is commonly used although various more advanced models, already known from X-ray diffraction, can also be applied to enhance the analysis. In this study a comparison is presented of IAM and TAAM (transferable aspherical atom model), the latter with the parameters of the Hansen-Coppens multipole model transferred from the University at Buffalo Databank (UBDB). By this method, TAAM takes into account the fact that atoms in molecules are partially charged and are not spherical. Structure refinements were performed on a carbamazepine crystal using electron structure-factor amplitudes determined experimentally [Jones et al. (2018). ACS Cent. Sci. 4, 1587-1592] or modelled with theoretical quantum-mechanical methods. The results show the possibilities and limitations of the TAAM method when applied to electron diffraction. Among others, the method clearly improves model fitting statistics, when compared with IAM, and allows for reliable refinement of atomic thermal parameters. The improvements are more pronounced with poorer-resolution diffraction data.

中文翻译：

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利用多极电子散射因子细化有机晶体结构。

由于在低温下对单个粒子进行成像以及从小有机分子或大分子的纳米晶体中获取电子衍射数据的方法的发展，电子显微镜正在发生分辨率的革命。可以实现分子结构的近原子甚至原子分辨率。这些方法的基础是由于样品的静电势而导致的电子束散射。为了分析这些高质量的实验数据，需要使用适当的原子散射因子。通常使用独立原子模型 (IAM)，但也可以应用从 X 射线衍射中已知的各种更先进的模型来增强分析。在这项研究中，对 IAM 和 TAAM（可转移非球面原子模型）进行了比较，后者使用从布法罗大学数据库 (UBDB) 转移的 Hansen-Coppens 多极模型的参数。通过这种方法，TAAM 考虑了分子中的原子部分带电且不是球形的事实。使用实验确定的电子结构因子振幅对卡马西平晶体进行结构精修[Jones 等人。（2018）。ACS中心。科学。4, 1587-1592]或用理论量子力学方法建模。结果表明 TAAM 方法应用于电子衍射时的可能性和局限性。除此之外，与 IAM 相比，该方法明显改进了模型拟合统计数据，并且可以可靠地细化原子热参数。对于分辨率较低的衍射数据，这种改进更为明显。