Dear Xiaozhou Liu,
In the "nfo-mfc_phicalc_map.inp" example file distributed with
X-plor 3.851 there is a typo. If nn=mm=1 (i.e. a difference map)
and SigmaA-weighting is used, then the centric reflections are set
to "mFo, PhiC" instead of "mFo-DFc, PhiC" on the following line:
do (diff = combine(fom * ampl(fobs), phase(fcalc)) )
( centric and sel=1 )
(this is done since for 2Fo-Fc maps, the amplitude of the centric
reflections should be set to mFo to minimize model bias instead
of 2mFo-DFc as for acentric reflections, but for difference maps
the amplitudes should be mFo-DFc both for acentric and centric
reflections). The result will be spurious density features.
To calculate a difference map (not 2Fo-Fc !) change:
do (diff = combine($nn * fom * ampl(fobs) -
$mm * dd * ampl(fcalc), phase(fcalc)) )
( acentric and sel=1 )
do (diff = combine(fom * ampl(fobs), phase(fcalc)) )
( centric and sel=1 )
to:
do (diff = combine($nn * fom * ampl(fobs) -
$mm * dd * ampl(fcalc), phase(fcalc)) )
( sel=1 )
or make something more clever if you want it to work with
both difference maps (Fo-Fc) and other maps (e.g. 2Fo-Fc).
Thomas
____________________________________________________________________________
Thomas Ursby
Molecular Biophysics Tel: (+46) 46 222.45.13
Chemical Centre (+46) 46 222.46.80 (Secretary)
Lund University (+46) 46 222.01.13 (MAX-lab)
P.O.B. 124 Fax: (+46) 46 222.46.92
S-221 00 Lund Email: thomas.ursby at mbfys.lu.se
Sweden WWW: http://www.mbfys.lu.se
(Visiting address: Getingevagen 60)
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