Abstract
It is a relatively easy task to the solution of the so-called phase problem in crystallography, by applying ab initio phasing methods for the efficiency of structure solution from single-crystal data. Their effective application to powder x-ray diffraction data is still a real challenge unless the size of the structure is moderate. The percentage of principal success hinges on a number of factors; included are the quality of the experimental pattern, the success of the pattern-decomposition programs, the quality of the extracted structure-factor from the experimental pattern via the Le Bail or Pawley methods, the normalization of structure-factor process, the experimental resolution and the straightforward of the phasing process. This paper aims at providing an overall overview of the reciprocal space RS methods (ab initio phasing methods of crystal structure) as well as the direct methods, Patterson function and maximum entropy methods. This paper will also describe the factors affecting phasing by reciprocal space methods and the limitation of reciprocal space methods. Those are available for carry out the structure solution, in order to provide a clear theoretical account, experimental practice and computing approaches regarding and describe an outline of the solution process of phase problem by powder X-ray diffraction, leads to the best structure solution using practical examples.
Highlights
Structure solution from powder x-ray diffraction data (PXRD) is considered to be a real challenge in crystallography
The peak overlapping in powder diffraction pattern leads to the amount of experimental information: small number of structure amplitudes that are measured in the powder experiment compared with the several thousand of a single crystal experiment
The aim of this paper is to provide, in particular an overview of different methods operate in reciprocal space
Summary
Structure solution from powder x-ray diffraction data (PXRD) is considered to be a real challenge in crystallography. The determination of the unit cell parameters is the primary step in structure solution from PXRD data, the cell-characterization process is called ‘indexing’ This later, by autoindexing methods, is normally put in to action, for which a number of computer programs are available; ITO [1], TREOR [2], DICVOL [3] and NTREOR09 [4]. The peak overlapping in powder diffraction pattern leads to the amount of experimental information: small number of structure amplitudes (several hundred) that are measured in the powder experiment compared with the several thousand of a single crystal experiment. Such problems define all the steps of the solution process
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