Computer programs PSSP and WinPSSP
The computer program PSSP [1] uses direct-space methods for the crystal structure solution of molecular solids from monochromatic X-ray powder diffraction data. Once the unit-cell parameters and space group symmetry of the material are known, the integrated intensities of the reflections are calculated using the Le Bail method [2] and the software GSAS or FULLPROF, and they are written into *.rfl or *.hkl files, respectively. A set of correlation coefficients for the integrated intensities of reflections close in 2theta, the refined peak positions, and FWHM are used to reconstruct the experimental powder diffraction pattern. The molecular (or fragment) geometry to locate in the unit-cell is obtained from databases or calculated, and it is stored in cif or Cartesian coordinates files. The files above are read by WinPSSP, and a set of structural parameters allowing the generation of trial crystal structure solutions is defined. WinPSSP calculates a large number of trial models and their diffraction patterns, which are compared with the “experimental” pattern through a cost function, which is minimized by the simulated annealing algorithm [3]. WinPSSP [4] is a windows version of PSSP, freely downloadable from http://users.uoi.gr/nkourkou/winpssp/. Finally, a Rietveld fit is carried out with the software GSAS.

Instructional videos
WinPSSP distribution site: https://www.youtube.com/playlist?list=PL7i87HzJlst4TnVdbzImJoTdgmzIQxnHv

Crystal structure solution of 2-ethoxybenzamide: https://www.youtube.com/playlist?list=PLzFrCI1KQr2OAoJk8o8UudwbXru85sOng

References

• [1]- S. Pagola and P. W. Stephens, J. Appl. Cryst. (2010) 43, 370-376. 
• [2]- Le Bail, A. (2005). Powder Diffraction, 20, 316–326. 
• [3]- Kirkpatrick, S., Gellatt, C. D. Jr & Vecchi, M. P. (1983). Science, 220, 671–680.
• [4]- S. Pagola, A. Polymeros, and N. Kourkoumelis, J. Appl. Cryst. 50 (2017) 293-303. https://onlinelibrary.wiley.com/doi/pdf/10.1107/S160057671601846X