Making ripples in the comparison of calculated and experimental maps for real-space refinement and assessment by analytic modelling of local resolution

Abstract

Our experimental knowledge of structure in atomic detail is derived from the electron density or electrostatic potential map interpreted as an atomic model. Conversely, we calculate the theoretical map from our model and comparison of both sources is used to refine (Urzhumtsev & Lunin, 2019) and improve this knowledge or assess its correctness. In this issue of IUCrJ, Urzhumtsev & Lunin (2022) revisit first principles underlying imperfections in the experimental maps in order to propose a map calculation with variables to account for atomic displacement and local resolution linked to each atom. The new maps reflect the observed inhomogenous resolution with superior accuracy and their expression is nearer to physical reality, along with the useful feature of simplifying the necessary calculation of derivatives with respect to all parameters.