Dear Rietvelders, I am working on a structure of a ferric sulfate, with triclinic symmetry and 50 atoms in the unit cell. We have both X-ray synchrotron and neutron data. At the moment, I am using constraints to keep the O-H bond distances and H-O-H angles within reasonable range.
One of the metal sites contains vacancies (2/3 occupied, 1/3 vacant), but the ligands (H2O) remain even if the metal is absent. As expected, the atoms of these water molecules have very high thermal factors, indicating split positions. The presence of vacancies also changes the hydrogen bonding scheme around this site. We have ab initio calculations explaining nicely what is going on on this position. My question is: Since I am already using the constraints, therefore somewhat imposing "my solution" on the structure, can I add more complexity to the refinement, using the results of ab initio calculations, and say that this is real? Or should I just be happy with the high thermal factors and the explanation from the calculations? Is there a way to know that the data are not providing any more results, and you are just forcing the outcome you like? Thank you for the answers, Juro Majzlan ------------------------ Juro Majzlan Department of Geosciences Princeton University Princeton, New Jersey 08544 USA
