The multipole model (MM) uses an aspherical approach to describe electron density and can be used to interpret data from X-ray diffraction in a more accurate manner than using the spherical approximation. The MATTS (multipolar atom types from theory and statistical clustering) data bank gathers MM parameters specific for atom types in proteins, nucleic acids, and organic molecules. However, it was not fully understood how the electron density of particular atoms responds to their surroundings and which factors describe the electron density in molecules within the MM. In this work, by applying clustering using descriptors available in the MATTS data bank, that is, topology and multipole parameters, we found the topology features with the biggest impact on the multipole parameters: the element of the central atom, the number of first neighbors, and planarity of the group. The similarities in the spatial distribution of electron density between and within atom type classes revealed distinct and unique atom types. The quality of existing types can be improved by adding better parametrization, definitions, and local coordinate systems. Future development of the MATTS data bank should lead to a wider range of atom types necessary to construct the electron density of any molecule.

中文翻译：

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来自理论和统计聚类 (MATTS) 数据库的多极原子类型：聚类分析中周围原子对电子密度的影响

多极模型 (MM) 使用非球面方法来描述电子密度，并且可用于以比使用球面近似更准确的方式解释 X 射线衍射数据。MATTS（来自理论和统计聚类的多极原子类型）数据库收集特定于蛋白质、核酸和有机分子中原子类型的 MM 参数。然而，尚未完全了解特定原子的电子密度如何对其周围环境作出反应，以及哪些因素描述了 MM 内分子中的电子密度。在这项工作中，通过使用 MATTS 数据库中可用的描述符（即拓扑和多极参数）进行聚类，我们发现了对多极参数影响最大的拓扑特征：中心原子的元素，第一邻居的数量, 和组的平面性。原子类型类别之间和内部的电子密度空间分布的相似性揭示了不同且独特的原子类型。通过添加更好的参数化、定义和局部坐标系，可以提高现有类型的质量。MATTS 数据库的未来发展将导致构建任何分子的电子密度所需的更广泛的原子类型。