How to perform ab initio Rietveld refinement to obtain chemical structure from PXRD data?

Ok, thanks to all in advance. I guess that i have gathered all important details to try to ab initio solve a structure. Hence,

1) first is to have good quality microcrystals

2) pack the sampler avoiding preferred orientation of microcrystals

3) obtain a good powder X-ray collection, perhaps as stated in DASH or EXPO user manuals documentation with, 2θ[=]° interval, & different counting times (s) as follows:

5.0 - 15.0 with 0.5

15.0 - 25.0 with 1.0

25.0 - 35.0 with 2.0

35.0 - 45.0 with 4.0

45.0 - 55.0 with 8.0

55.0 - 65.0 with 16.0

4) inspect diffraction specially at higher 2θ values (eg. beyond 25°)

5) thoroughly & carefully remove background

6) index cell with DICVOL or so on

7) revise cell parameters, e.g. not very short nor very large geometric data should be used for the correct cell determination, revise chiral space groups when needed

8) extract intensities with Pauley or LeBail procedures

9) viewing & revise obtained peak positions, as well as systematic absences, corroborating the correct space group & symmetry

10) provide a starting molecular model

11) define rotatable bonds for conformational space definition (beware of stereoisomers & special positions they need to be settled)

12) fix geometries in most low rotation moieties or rings

13) perform simulated annealing (or related strategies), which takes into account the molecular position, orientation and conformation for random search

I am at this point by now. I will complete the list forthcoming.

Best regards to all again.

Hiram

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