A modified version of the Busing-Martin-Levy least squares program for the direct fitting of structures to powder diffraction patterns by the method of profile analysis

Abstract

The Busing-Martin-Levy (BML) crystallographic least squares program has been modified to handle the case of the overlapping diffraction data encountered in powder patterns. Each count along the scan is treated as a single observation and the pattern is considered to be the superposition of the (h,k,l) Gaussian peaks, as in the method of Rietveld (Acta Cryst., 22, 151 (1967)). In this way the structure is fitted directly to the diffraction pattern, while details of the profiles are not lost. For this reason, together with the fact that a larger number of observations are used, the method is superior to conventional refinements with integrated intensities (which can also be done with the present program).