Interactive visualization of electron density slices

A new tool has been developed to aid in the visualization of electron density in crystals or from quantum chemistry calculations. It displays the fine details of the electron density on a plane and the three-dimensional model of the molecule at the same time. The program enables the user to examine the details of weak or irregular features. Such features frequently occur in low-resolution maps, where they determine the correct tracing of a protein backbone. In high-resolution maps, solvent regions are difficult or impossible to observe using isosurfaces. The tool has been integrated into an existing molecular visualization package (PyMol) making it possible to observe and interact both with a structure model and the electron density slices freely, simultaneously and independently. This visualization model fills a gap in the visualization methods available to crystallographers and others who work with electron density maps.