Hi everyone, I ran a DEN refinement of my low resolution structure (3.6) to improve my model. I typed in the following command: phenix.den_refine model.pdb data.mtz den.reference_file=reference.pdb reference.params with reference.params saying: refinement.reference_model.reference_group { reference = chain A and resseq 1:953 selection = chain A and resseq 1:953 } refinement.reference_model.reference_group { reference = chain B and resseq 1:687 selection = chain B and resseq 1:687 } because the reference file only contains chain A and chain B. Unfortunately I obtained much worse R factors then with a regular refinement: Start R-work = 0.2798, R-free = 0.3176 Final R-work = 0.3733, R-free = 0.4089 Does someone have an idea what could have go wrong? Thanks,