[phenixbb] Problematic dataset

[Lucas Bleicher]

I have a 1.9A dataset that could, in principle, be
used to a molecular replacement solution. Phaser finds
a solution which yields reasonable map to model
agreement, but R factors do not fall down from values
greater than 40%.

It looked like a P21 (systematic absences are clear),
so there was not much options on symmetry. I
reprocessed the dataset in P1 and ran phenix.xtriage,
and these lines called my attention:

---------------------------------------------
 Analysing possible twin law :  -h,-k,l
---------------------------------------------


Results of the H-test on a-centric data: 

 (Only 50.0% of the strongest twin pairs were used)

mean |H| : 0.053   (0.50: untwinned; 0.0: 50% twinned)
mean H^2 : 0.005   (0.33: untwinned; 0.0: 50% twinned)
Estimation of twin fraction via mean |H|: 0.447
Estimation of twin fraction via cum. dist. of H: 0.449


---------------------------------------------
 Analysing possible twin law :  -h,-h+k,-l
---------------------------------------------


Results of the H-test on a-centric data: 

 (Only 50.0% of the strongest twin pairs were used)

mean |H| : 0.093   (0.50: untwinned; 0.0: 50% twinned)
mean H^2 : 0.015   (0.33: untwinned; 0.0: 50% twinned)
Estimation of twin fraction via mean |H|: 0.407
Estimation of twin fraction via cum. dist. of H: 0.407

---------------------------------------------
 Analysing possible twin law :  h,h-k,-l
---------------------------------------------


Results of the H-test on a-centric data: 

 (Only 50.0% of the strongest twin pairs were used)

mean |H| : 0.085   (0.50: untwinned; 0.0: 50% twinned)
mean H^2 : 0.013   (0.33: untwinned; 0.0: 50% twinned)
Estimation of twin fraction via mean |H|: 0.415
Estimation of twin fraction via cum. dist. of H: 0.417


=========

I have never dealt with twinned datasets before. Is
there something I could try to do to obtain useful
data from this?

Lucas

P.S.: Unfortunately, growing more crystals is not an option.


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