Gram-Charlier development of the atomic displacement factors into mineral structures: The case of samsonite, Ag4MnSb2S6

摘要

During structure solution of Ag-, Cu-bearing minerals it is quite common to observe disorder. Ag+ and Cu+, indeed, can occur in different, but overlapping sites. The typical way to deal with these kind of minerals in structure determination is to use a split-atom model. This approach, however, has several disadvantages and may give rise to ambiguities. A solution to the problem can be the use of higher order tensor elements in the expression of the structure factors (the "non-harmonic approach"). This alternative approach gives, in cases of highly overlapping electron densities, an equivalent description of the split-atom model.