Hi Shane,

I've got a question related to refinement of an ion on a special position. I have a structure with an atom placed squarely on the C2 axis. I've been able to get a mostly-reasonable model by dropping in the ion at 0.5 occupancy and turning off repulsion for the ion in question, as Pavel describes here. It almost completely works.

OK, all sounds good so far!

The thing I find now is that during refinement there can still be some random drift of the atom away from the symmetry axis, splitting from its symmetry ghost, while I know that it should stay perfectly coincident.

Hm.. this is odd and I'm pretty sure the code that handles this makes sure atoms on special position should stay there perfectly (no drifting).

My resolution is 3.1 and there's no indication of a multiple conformation, so a split isn't justified. The most parsimonious model should place the ion exactly on the C2.

All true!

Looks like I need to investigate this in greater detail.. Would it be possible to send me model and data files, as well as any ligand cif (if used) and that will be a good start for me. I'm traveling next week, so if I get files today I may be able to respond before my travels.

Pavel