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Re: [ccp4bb]: Data processing
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On Fri, 30 Mar 2001, Carlo Ciatto wrote:
> Well, it must be triclinic...but the refined cell is the following:
> 89.211 89.214 150.819 90.000 89.989 87.153 ----> a=b, alpha=beta=90.
Well, it could genuinely be triclinic with two 90.0 degree angles - the
crystal system only imposes the metric values on the cell parameters -
they are "necessary but not sufficient"; it's the internal symmetry that
defines the crystal system (an ultimately space group). Many
crystallographers who have collected data on more than a few crystals have
an example of beta = 90.000 for a monoclinic cell, and I'm sure there are
some out there who have triclinic cells with three 90.00 degree angles.
> Any ideas or suggestions? Where should one look for possible problems or
> mistakes (before scaling)? I must confess my unease with symmetry, maybe
> the Denzo table is showing me something that I cannot see.
Something to look for would be incorrect main beam position. Have a look
at the images and see if there is apparent symmetry of intensities with
the indices shifted by + or - 1.
Other things could be high absorption coupled with a badly centred
Dr Harry Powell, MRC Laboratory of Molecular Biology, MRC Centre, Hills
Road, Cambridge, CB2 2QH