ASTRA 4.0 Program: Data Reduction for Obtaining Structure Results of Extreme Accuracy

Unique methods for processing diffraction data, which guarantee extreme accuracy and reliability, have been implemented in the ASTRA 4.0 software package. The central (data-forming) element is a program for averaging intensities of repeated and equivalent reflections. The ASTRA averaging algorithm makes it possible to calculate the average intensity and its standard uncertainty, which correspond to normal distribution law for errors in data. Such data yield an unbiased estimate of the parameters of refined structural model at minimum reliability factors. To make the averaging program successfully operate, one must introduce all corrections for anisotropic effects into the reflection's intensities. The following stages of investigation are considered: sample preparation; calibration of diffractometer; and correction for absorption, thermal diffuse scattering, and simultaneous reflections. A significant advantage of the proposed approaches is proven on several examples.