As far as I know map coeffiicient correspond to detwinned data. But
using detwinned data may not be a good idea.
It would be good to see what are R factor. Another thing to consider
is that different program may use different flags for free R and it
may cause some problem.
What are Rfactors, completeness, percentage of freeR reflections?
These are printed by all programs.
If your solution is wrong and you are using twin refinement even if
you do not have twinned crystals your R factor can be as low as 50%
(that is theoretical limit for random Rfactor when one data are from
twinned and another from untwinned crystals). If you have perfect twin
and you are modelling twin (using twin refinement) then your random
Rfactors can be even smaller.
regards
Garib
On 16 Mar 2009, at 11:51, Eleanor Dodson wrote:
But dont all twinned refinement programs output detwinned terms for
a map?
Certainly REFMAC and SHELX do.
Eleanor
Clemens Steegborn wrote:
Hi Walter,
You should definitely detwin data for map calculation if you have a
significant twinning fraction (and only for maps; keep using the
twinned
data set for refinement). We use the CCP4 program detwin. BUT if
Shelxl
gives bad density, maybe that's simply what you have, a bad density
map -
because output from Shelx is already detwinned!
BTW, we observed that different programs handled different cases
differently
well; I would suggest ALWAYS to try more than one program, and also
to try
Phenix ...
Best
Clemens
-----Ursprüngliche Nachricht-----
Von: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] Im Auftrag
von
Walter Kim
Gesendet: Monday, March 16, 2009 7:22 AM
An: CCP4BB@JISCMAIL.AC.UK
Betreff: [ccp4bb] Twinned data and maps
Hi again,
Thanks for your insight into refinement tools for twinned data. I
have a
couple of twinned data sets that are nearly perfectly
pseudomerohedrally
twinned. I've begun to refine my data in Refmac5 (using the
automated twin
refinement), CNS (using the twin inputs) and Shelxl; I'm testing
out the
different refinement programs to evaluate the best strategy for the
refinement. However, I would like to start making maps.
1. Refmac5 - outputs an mtz that is model-biased
2. CNS - maps made via model_map_twin.inp are poor
3. Shelxl - the maps generated in coot from the.fcf file are poor
Are there better ways to make cleaner maps with my twinnned data
that are
less model-biased that I can try to build into? Should I detwin the
data and
make maps from that (but continue to refine against the twinned
data)?
Thanks,
Walter
