These papers might help:
J. Appl. Cryst. (1997). 30, 396-399, F. M. D. Vellieux and B. W. Dijkstra
J. Appl. Cryst. (1997). 30, 400-401, F. M. D. Vellieux
Speaking of 3fo2fc or 5fo3fc, ... etc maps (see classic works on this
published 30+ years ago), I guess the main rationale for using them in
those cases arises from the facts that
2Fo-Fc = Fo + (Fo-Fc),
3Fo-2Fc = Fo +2(Fo-Fc)
and so on, and not from whether the one map is more (or less) model
biased than the other one.
Randy Read (1986) showed that 2mFo-DFc is least model biased. The m and
D coefficients has to be computed using test reflections (Urzhumtsev et
al, 199?). To be precise, it is actually
2mFo-DFc for acentric reflections
and mFo for centric reflections
Pavel.
On 7/29/10 12:12 PM, Hailiang Zhang wrote:
Hi,
I frequently find 3mFo-2DFc maps have been used for model building. I am
not sure whether they have less model bias than 2mFo-DFc maps, and I
appreciate for any references.
Best Regards, Hailiang
