A new aspherical scattering factor formalism has been implemented in the crystallographic least-squares refinement programSHELXL. The formalism relies on Gaussian functions and can optionally complement the independent atom model to take into account the deformation of electron-density distribution due to chemical bonding and lone pairs. Asphericity contributions were derived from the electron density obtained from quantum-chemical density functional theory computations of suitable model compounds that contain particular chemical environments, as defined by the invariom formalism. Thanks to a new algorithm, invariom assignment for refinement inSHELXLis automated. A suitable parameterization for each chemical environment within the new model was achieved by metaheuristics. Figures of merit, precision and accuracy of crystallographic least-squares refinements improve significantly upon using the new model.

中文翻译：

---

SHELXL 的非球面散射因子 – 模型、实现和应用


晶体学最小二乘细化程序 SHELXL 中实施了新的非球面散射因子形式。该形式依赖于高斯函数，并且可以选择性地补充独立原子模型，以考虑由于化学键和孤对而导致的电子密度分布的变形。非球面贡献源自电子密度，该电子密度是通过对包含特定化学环境的合适模型化合物进行量子化学密度泛函理论计算而获得的，如不变形式主义所定义。得益于新算法，SHELXL 中的优化分配已实现自动化。通过元启发法为新模型中的每个化学环境实现了合适的参数化。使用新模型后，晶体学最小二乘精修的品质因数、精度和准确度显着提高。