Let's say there are two orientations of a ligand for which occupancies need to be refined. By default, the sum of the two will be fixed at 1.0. From quick look at the manual, the only way to have the sum(occ) at lower level is to reset main.occupancy_max. However, this will probably affect all the atoms for which occupancies are refined, which is undesirable (while ligand may have total occupancy of <1, alternate conformers for protein residues should always add up to 1). Am I missing something or the only way to get this done is to refine twice - once only for ligand occupancy, and then for the rest of the model. And what if total occupancy of the ligand is unknown? Is there a way to allow sum(occ) to be anywhere between 0 and 1? -- "I'd jump in myself, if I weren't so good at whistling." Julian, King of Lemurs