ASTRA -: a program package for accurate structure analysis by the intermeasurement minimization method

ASTRA2.0 is a program package for single-crystal structure research using different experimental conditions and radiation of different types ( X-rays, neutrons and electrons). The package includes programs for data collection optimization, data reduction, structural parameter refinement and electron density plotting. The expression that is responsible for minimization of the difference between reduced measurements is included in the goal function of the refinement program. The refinement program is based on an adaptive nonlinear least-squares method. The crystal structure is described by a detailed model for electron density analysis. ASTRA uses a multipole model up to eighth order for the aspherical electron density description, an anharmonic model up to sixth order for the description of atom displacement and a model of mixed atomic positions for the description of atomic replacement. Refinement of the structural parameters using data of precession electron diffraction and the Bloch-wave method to account for multiwave scattering is realized. Tools for refinement automation are included in ASTRA.