>There does indeed appear to be a tendancy for the SHELXC values to become
>slightly negative at the high resolution end, i.e. when a value of zero would
>be expected for pure noise, so maybe it is something more fundamental?!
I think it is something more fundamental, and I've just explored whet
Not to harp on this too much, but I was helping a colleague today on an
unrelated structure, and his dataset also showed negative CCanom's in all bins.
I am now suspecting that there might be an actual bug in Aimless. Anyone else
also seeing this?
Jacob
ct: RE: [ccp4bb] Negative CCanom
[Sorry, typography was off a bit in the last one]
Here is the answer, I think, to why twinning leads to negative CCanom:
In fact, in any case in which the anomalous signal changes as a function of
exposure, CCanom can be negative.
The usual case is radiation damage
AM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] Negative CCanom
Hi Jose,
I don't think that Jacob's point was about XDS producing negative CC1/2-anom ,
since he was not using XDS.
Concerning your observations: if there is zero anomalous signal then the
CC1/2-anom is _not_ expected to
>No, it's just merohedral - the true and the apparent spacegroup belong to the
>same pointgroup.
Even if it were pseudo-merohedral it would be a superposition of reflections,
with addition of their intensities.
Well, if there are several apposed crystals as hypothesized before, where they
are c
July 17, 2015 8:00 AM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] Negative CCanom
Am 17. Juli 2015 00:00:11 MESZ, schrieb "Keller, Jacob"
:
>>Jacob's case is twinning in P3(2)12 making the data appear as P6(2)22,
>so it is indeed a rotation by 180°.
>
>Yes, this al
[Sorry, typography was off a bit in the last one]
Here is the answer, I think, to why twinning leads to negative CCanom:
In fact, in any case in which the anomalous signal changes as a function of
exposure, CCanom can be negative.
The usual case is radiation damage:
Consider, to start, four in
Here is the answer, I think, to why twinning leads to negative CCanom:
In fact, in any case in which the anomalous signal changes as a function of
exposure, CCanom can be negative.
The usual case is radiation damage:
Consider, to start, four independent measurements of one reflection, two I+ an
>Jacob's case is twinning in P3(2)12 making the data appear as P6(2)22, so it
>is indeed a rotation by 180°.
Yes, this all fits together nicely. If I understand correctly, this would make
my crystals a blend of mero- and pseudo-mero-hedral, so involving I's and F's,
no?
JPK
