riceviamo dal Prof. Immirzi questo messaggio che vi inoltriamo:
I am presently studying methods for solving structures through random search and genetic algorithms. The aim is to solve, always using internal coordinates, molecular or polymeric structures of known connectivity, using few data (also fiber data!) at low resolution (less than say 1.5-2.0 A). The major interest is in powder diffraction, but also single-crystal problems, suffering of scarce resolution, can be undertaken with this approach.
If you have studied such problems, without success with traditional approaches (direct methods, Patterson, etc.), maybe that this innovative approach can run well. I am very interested in establishing collaborations, not for producing articles, but only for improving the method and the program.
There are not definite upper limits. Studies done on structures already known gave good result up to 50-60 independent non H atoms, with a lot of conformational freedom, always using low resolution data. Paradoxically intricated and flexible molecules are more promising than simple and rigid molecules. I am tempted to undertake larger problems. The true limit is not the number of atom but the number of free torsion angles. 30-40 torsion angles do not scare me too much.
Program information is available on J. Chem. Info. Model. 2007, 2263-2265, in J. Appl. Crystallogr. 2007, 1044-1049 and at the web address http://www.theochem.unisa.it/try.html
Random-search and genetic algorithms are however not yet published; a paper, based on known structures, is in preparation.
If you think this message of interest, write me please. Data as .fcf files are welcomed. Of course lattice constants and symmetry are needed. If molecular connectivity is uncertain, but there are few alternatives only, the route is even practicable.
With the best wishes
University of Salerno Italy