Have a look at GRINSP (Geometrically Restrained INorganic
Structure Prediction) :
http://sdpd.univ-lemans.fr/grinsp/
This is a beta version 0.9, but it can already "predict" a huge
quantity of complex structures with one simple formula : SiO2.
A database of "predicted" structures will appear soon as a
subset of the COD (~200 entries for next monday or tuesday,
predicting only < 2000 A**3 cells for the moment ;-).
Have fun with GRINSP !
Armel