Commission on Crystallographic Computing

Data reduction: Mosflm

Harry Powell
MRC-LMB, Cambridge, UK

Integration of diffraction images is centred around three basic operations, i.e. indexing the images, refining the crystal and instrument parameters, and measuring the intensities of the Bragg diffraction maxima. In Mosflm, these functions are performed using values which are optimized based on images from each individual dataset, rather than requiring the user to provide them or using pre-set defaults.

Mosflm uses an FFT based method for autoindexing images that gives real space cell parameters and the crystal orientation directly. Refinement of crystal and instrument parameters by the use of different residuals (i.e. postrefinement and positional refinement, respectively) gives an independent refinement and removes the possibility of strong correlations which can lead to instabilities. The intensities themselves are measured using two dimensional profile fitting; the methods used to optimize this measurement and to distinguish "spot" regions from background and from other spots will be discussed.

Tutorials will focus on the implementation of these different processes, and in particular their optimization within the program.

These pages are maintained by the Commission Last updated: 15 Oct 2021