Abstract: X-ray single-crystal structure analysis serves as a fundamental technique for molecular structure determination. Conventional refinement methods relying on the independent atom model fail to account for non-spherical electron density distributions in chemical bonds, resulting in substantial positional errors for hydrogen atoms. The implementation of non-spherical atomic models not only enhances refinement outcomes but also enables accurate localization of hydrogen atoms. This work presents the methodology of non-spherical structure refinement, employing the NoSpherA2 refinement tool integrated within the Olex2 platform. Through a practical demonstration using a cocrystal system, we illustrate the superior precision achieved with this approach. This case study provides chemistry students and crystallography researchers with practical guidance for implementing non-spherical refinement techniques while advancing their knowledge in quantum crystallography.

Key words: Crystallography, Single-crystal structure analysis, Non-spherical structure refinement, NoSpherA2