Isn't automatically included fabricated data for missing reflections
a really bad idea for anisotropic data where most reflections are
"missing" at high resolution? Shouldn't there be a big flashing red
flag alerting the user to what's been done?
Phoebe
At 01:22 PM 3/26/2007, Edward A. Berry wrote:
Actually I was thinking of a somewhat earlier paper:
Rayment,I. Molecular relacement method at low resolution:
optimum strategy and intrinsic limitations as determined
by calculations on icosahedral virus models.
Acta Crystallogr. A 39, 102 116 (1983).
But thanks for bringing the Caliandro et al. paper to my attention.
Thanks also to Fred. Vellieux for his comments, and to Pete Dunton
for explaining to me that while fft doesn't do fillin by default,
the 2MFo-DFc map coefficients from refmac5 do have fillin values
for the missing reflection, making model bias a problem when
many missing residues are included.
Now I understand Petrus's question.
Ed
Michel Fodje wrote:
You are probably referring to the following works:
Caliandro et al, Acta Cryst. D61 (2005) 556-565
and Caliandro et al, Acta Cryst. D61 (2005) 1080-1087
in which they used density modification to calculate phases for
unmeasured reflections, and used the phases to extend the resolution by
calculating rough estimates unmeasured amplitudes. Using this technique
they actually could improve the electron density.
If I'm not mistaken, George Sheldrick has implemented this "Free Lunch"
algorithm in SHELXE.
/Michel
On Fri, 2007-03-23 at 08:05 -0800, Edward Berry wrote:
If instead you allow the missing F's
to "float", calculating them on each cycle from the previous map
using the fillin option, someone has shown (don't have the
reference handy at the moment) that the F's tend toward the true F's
(in the case that they weren't really missing but omitted as part
of the test).
Ed
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Phoebe A. Rice
Assoc. Prof., Dept. of Biochemistry & Molecular Biology
The University of Chicago
phone 773 834 1723
fax 773 702 0439
http://bmb.bsd.uchicago.edu/index.html
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