Abstract
A method is presented that modifies a 2mFobs - DFmodel σA-weighted map such that the resulting map can strengthen a weak signal, if present, and can reduce model bias and noise. The method consists of first randomizing the starting map and filling in missing reflections using multiple methods. This is followed by restricting the map to regions with convincing density and the application of sharpening. The final map is then created by combining a series of histogram-equalized intermediate maps. In the test cases shown, the maps produced in this way are found to have increased interpretability and decreased model bias compared with the starting 2mFobs - DFmodel σA-weighted map.
Highlights
An electron density map is typically an important step in obtaining an atomic representation of a crystal structure, or the map itself may serve as the model of the contents of the crystal
feature-enhanced map (FEM) maps are expected to be less model-biased than the starting maps as they are filtered by the composite residual OMIT map
The Fourier maps routinely used in crystallographic structure solution are never perfect owing to errors in both the
Summary
An electron (or nuclear) density map is typically an important step in obtaining an atomic representation of a crystal structure, or the map itself may serve as the model of the contents of the crystal. In either case the quality of the map affects its utility. We consider a desirable map to be one that accurately represents the actual electron (or nuclear) density in an average unit cell of the crystal. There are at least three different factors that affect the quality of crystallographic maps and their interpretation. The finite resolution and the incompleteness of measured reflections and errors in experimental data and crystallographic model parameters are major contributors to poor map quality. These errors may obscure or corrupt the signal, making meaningful interpretation difficult or even impossible
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