The various steps necessary for crystal structure determination from powder data are the following: a) unit cell indexation; b) space group determination; c) crystal structure determination; d) crystal structure refinement by least squares-Rietveld refinement techniques. In the last years strong advances in the methods allowed to solve crystal structures of size forbidden  for old techniques. Also the accuracy of the final molecular models improved.  EXPO2008 contains various advances with respect to the previous release. They concern:

a) the unit cell indexation. The search has been made more efficient and exhaustive.

b) The space group determination. The use of the joint probability distribution method has been made more efficient by combining it with the automatic control of the experimental pattern.

c) Crystal structure determination. A recent theory aiming at reducing the effects of the limited resolution (so important when powder data arise from organic samples) in the electron density maps has been implemented in EXPO2008. The capacity of EXPO2008 of solving organic crystal structures from powder data, even at non- atomic resolution and via laboratory diffractometer data,  reached now a new powerful standard.

In case in which the molecular geometry is known, EXPO2008 customers  may use a robust simulated annealing algorithm.

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1. Resolution bias correction and crystal structure solution from powder data
2. MAD techniques applied to powder data: The method of the joint probability distribution functions