Completion of the Crystal Structure and Preliminary Refinement

Often the least-squares refinement is combined with an EDM (electron density modification) procedure the advantage is that it is not necessary to interpret electron density peaks in terms of atomic species. In practice the map is modified by a suitable function g to obtain a better representation p of the structure  

The function g is designed for exploiting positivity and atomicity of the electron density (the same information exploited in reciprocal space by the probabilistic formulae estimating structure invariants). Therefore the inversion of p is expected to produce better phase values than those used for calculating the map p. 

The above techniques have to be optimized for application to powder diffraction data. In particular  

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