Hi Ian,
> You have to be careful here because believe it or not, not all
> programs output the same coefficients for 'minimal bias' maps, so
> depending on which program Hailiang is using for SF
> calculation/refinement he may or may not get the right answer! You
> are assuming the difference map coefficient is (mFo-DFc) for both
> acentrics& centrics so you are expecting to calculate:
>
> 3mFo-2DFc = (2mFo-DFc) + (mFo-DFc) for acentrics
> 2mFo-DFc = Fo + (mFo-DFc) for centrics
>
> However as I have been at pains to point out on numerous occasions the
> correct difference map coefficient is 2(mFo-DFc) for acentrics (i.e. 2
> times half the peak height from an acentric mFo-DFc map), and
> (mFo-DFc) for centrics (i.e. 1 times the full peak height from a
> centric mFo-DFc map). This fact tends to be obscured if you think of
> it as Fo+(Fo-Fc) instead of Fc+2(Fo-Fc), which was my real objection
> to thinking of it in the way Pavel suggested.
... although it's coded right in PHENIX, that is 2(mFo-DFc) for
acentrics and (mFo-DFc) for centrics.
> I can't speak for phenix.refine, I suspect
> it gets it completely correct, since Pavel is on the case!
Yes Ian, it is correct there -;) Actually, we discussed it last year or
so, and you explained me the rationale for these 1 and 2 coefficients,
thanks!
Pavel.
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