Structure analysis by reduced data. IV. IEM—A new program for refinement of structure models of crystals

Abstract

A new program for the refinement of models of atomic structures by the X-ray, neutron, and electron diffraction data has been described. The program is based on a special form of the goal function including the term responsible for minimizing the difference between the normalized measurements [the interexperimental minimization (IEM) method] and the adaptive nonlinear algorithm of minimization based on the Lavrent’ev-Levenberg-Marquardt regularization. As a result, it became possible to determine a new solution to the problem different from that obtained by the classical least squares method. To a large extent, the program allows one to overcome the effect of parameter correlations on the procedure of refinement and the results obtained. The test of the program on 17 experimental data sets showed the fast and stable convergence in all the cases. Under the identical initial conditions, the new program provided lower reliability factors for most of the crystals studied.