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hmmm - in the ideal world with perfect data and a twin factor < 0.5 you would detwin your data before trying sad or mad.. But detaining inevitably increases the Sigmas so a weak signal can be lost.. The lab philosophy was - if you need to do expel phasing, and the data are twinned look for another crystal … But that may be too negative. You could try it and see if the phasing improved. Eleanor On 1 April 2016 at 21:40, Keller, Jacob <[log in to unmask]> wrote: > Dear Crystallographers, > > It occurred to me that SAD/MAD would work much better by incorporating > twinning into the HA finding/refining/phasing stage, since the Bijvoet > differences could be split according to the twinning fraction and/or the > HA's would be transformed by the twin operator and weighted by alpha and > (1-alpha). I believe twinning is not currently modeled during this stage, > even though for twinned structures this would dramatically improve things > almost to the level of untwinned data, I think. Twin fractions could be > determined at the HA stage, then everything would go more smoothly. Any > thoughts of such an implementation? Perhaps Shelx does this since 1969 or > something? > > I thought of this because I saw some really deep "holes" in the Phaser > output from a twinned dataset, and think these might be the evil other twin > sneaking in? > > JPK > > > ******************************************* > Jacob Pearson Keller, PhD > Looger Lab/HHMI Janelia Research Campus > 19700 Helix Dr, Ashburn, VA 20147 > email: [log in to unmask] > ******************************************* >