Difficult datasets

Small-molecule and low resolution protein datasets have few reflections per frame. Therefore, the multitude of parameters describing the diffraction experiment probably needs to be reduced. This means that e.g. the following parameters may need adjustment (typical values are given): most importantly

• DELPHI=45  ! to base reflection profiles and refinements on more reflections - try this first if yo get error messages in the INTEGRATE step

and you may also try

• NBATCH=4  ! to reduce the number of scale factors
• REFINE(INTEGRATE)= ! do not refine anything in INTEGRATE; be sure to recycle GXPARM.XDS to XPARM.XDS
• CORRECTIONS= ABSORB  ! don't try to correct for MODULATION and DECAY in scaling

Furthermore, you may try to recycle GXPARM.XDS to XPARM.XDS, and to grab the lines e.g.

BEAM_DIVERGENCE=   2.067  BEAM_DIVERGENCE_E.S.D.=   0.207
REFLECTING_RANGE=  2.303  REFLECTING_RANGE_E.S.D.=  0.329

from INTEGRATE.LP and to insert them into XDS.INP .