TRY, a new computer program for crystal structure analysis from diffraction data based on internal coordinates and on a molecular modelling procedure free of redundant coordinates

Abstract

A procedure is described which allows structure modelling using a number of internal coordinates that does not exceed the number of degrees of freedom of the problem. The modelling then becomes a strictly analytical procedure and structural refinement from diffraction data can be carried out avoiding the use of singular matrices. A practical `symbolic language' with a simple syntax allows easy molecular building even in intricate cases. Based on this procedure, a new computer program for the study of crystal structures (TRY), particularly suited for fibrous polymers, has been created. The program is available at http://www.theochem.unisa.it/try.html.

Constraints and restraints in crystal structure analysis

“…This applies of course in difficult cases, with a low data-to-unknown ratio. As discussed elsewhere (see Immirzi, 2007b), there is a general rule, which is applicable to all molecular crystals, for choosing the i.c. correctly: include all bond lengths among the i.c., then choose the other i.c.…”