Re: AMORE

[Eleanor Dodson <ccp4@yorvic.york.ac.uk>]

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I totally approve of your caution in processing the data i P222; systematic
absence analysis can be confusing, and a molecular replacement search is an
excellent way of distinguishing which possible symmetry is correct.
 But you have only tested half the necessary set. As phil Jeffries said; as
well as
 P222 ( 16) P2221 (17) P21212 (18) and P212121 (19) you need to test
 P2122 P2212 P21221 and P22121.
 The $CLIBD/symop.lib has been extended to include these options:

Here are the stdd ones already there:
16 4 4 P222 PG222 ORTHORHOMBIC 'P 2 2 2'
 X,Y,Z
 -X,-Y,Z
 -X,Y,-Z
 X,-Y,-Z
17 4 4 P2221 PG222 ORTHORHOMBIC 'P 2 2 21'
 X,Y,Z
 -X,-Y,1/2+Z
 -X,Y,1/2-Z
 X,-Y,-Z
18 4 4 P21212 PG222 ORTHORHOMBIC 'P 21 21 2'
 X,Y,Z
 -X,-Y,Z
 1/2-X,1/2+Y,-Z
 1/2+X,1/2-Y,-Z
19 4 4 P212121 PG222 ORTHORHOMBIC 'P 21 21 21'
 X,Y,Z
 1/2-X,-Y,1/2+Z
 -X,1/2+Y,1/2-Z
 1/2+X,1/2-Y,-Z

 And here are the extras:
1017 1 1 P2122 PG222 ORTHORHOMBIC 'P 21 2 2' !(unique axis a)
 X,Y,Z * -X,Y,-Z * 1/2+X,-Y,-Z * 1/2-X,-Y,Z
2017 1 1 P2212 PG222 ORTHORHOMBIC 'P 2 21 2' !(unique axis b)
 X,Y,Z *  X,1/2-Y,-Z * -X,1/2+Y,-Z * -X,-Y,Z
2018 1 1 P21221 PG222 ORTHORHOMBIC 'P 21 2 21'  !(unique axis b)
 X,Y,Z * -X,Y,-Z * 1/2+X,-Y,1/2-Z * 1/2-X,-Y,1/2+Z
3018 1 1 P22121 PG222 ORTHORHOMBIC 'P 2 21 21'  !(unique axis a)
 X,Y,Z *  X,-Y,-Z * -X,1/2+Y,1/2-Z * -X,1/2-Y,1/2+Z



 Add these to your symop.lib, or make your own copy, then test the other four
as well.

 All spacegroups are correct for reflections with h,k,and l even, so you always
get a reasonable TRAFUN correlation, but it should be much better fror the
correct spacegroup.

 Once you have chosen which it should be you probably should reindex the
crystal to get a standard setting.

 ie move hkl to klh or lhk to make sure the 21 axes are in the standard system.

OK? Eleanor Dodson

-- 
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Eleanor J.Dodson, Chemistry Department, University of York, U.K.
Tel: Home +44 (1904) 42 44 49, work:  +44 (1904) 43 25 65
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