Refinement of macromolecular structures against neutron data withSHELXL2013

Abstract

Some of the improvements inSHELX2013makeSHELXLconvenient to use for refinement of macromolecular structures against neutron data without the support of X-ray data. The new NEUT instruction adjusts the behaviour of the SFAC instruction as well as the default bond lengths of the AFIX instructions. This work presents a protocol on how to useSHELXLfor refinement of protein structures against neutron data. It includes restraints extending the Engh & Huber [Acta Cryst.(1991), A47, 392–400] restraints to H atoms and discusses several of the features ofSHELXLthat make the program particularly useful for the investigation of H atoms with neutron diffraction.SHELXL2013is already adequate for the refinement of small molecules against neutron data, but there is still room for improvement, like the introduction of chain IDs for the refinement of macromolecular structures.