This is precisely why SHELX always used the coordinates of the general
position (LATT+SYMM) to define the space group rather than a name or number.
George
On 22/07/20 14:15, Ian Tickle wrote:
Hi David
The problem is that the PDB incorrectly used the H lattice symbol
(without consulting any crystallographers AFAIK) for the hexagonal
R-centred cell when it had already been in use for many years for the
triply-primitive setting of P3, so now we have this confusion between
MX & XRD/powder usage. It's probably now too late to do anything about
it. Simply put: in XRD/powder software H3 is #143 as originally
specified in IUCr Int. Tab.; in MX software H3 is #146.
What should have been used are the Hermann-Mauguin symbols for the two
R3 cells: R3:r and R3:h (see the syminfo.lib file).
This is a constant confusion between the standard symbol (i.e. one of
the 230 space-groups in their standard settings) and the setting
symbols. Other common examples are space group #5 with standard
symbol C2 which has a number of alternative settings A121, B112, C121,
I121 etc., and standard symbol P21212 with settings P22121, P21221 and
P21212, all of which are equally valid. The conventional IUCr choice
of setting is determined by the relative cell lengths (as far as
possible c >= b >= a) and the cell angle (which in monoclinic cells
should always be chosen >= 90 and closest to 90). In practical
crystallography it's the setting symbol that matters; the standard
symbol is relevant only for classification, so in practice only the
setting symbols should be used/
Cheers
-- Ian
On Wed, 22 Jul 2020 at 12:32, David Vizarraga Revuelto
<dvr...@ibmb.csic.es <mailto:dvr...@ibmb.csic.es>> wrote:
Dear all,
Let me ask a question about the P3,H3, R3 space group annotations.
I had the idea that H3 was the recommended annotation for the
hexagonal representation of R3 (space group number 146). However,
in the Birbeck space groups web page (attached) H3 is associated
with the space group number 143 corresponding to P3. Similarly for
all the other H groups assigned in the page. Moreover in the
web page none of the R space groups is assigned to an H annotation.
H3 corresponds to 143 or to 146?
Is there a space group 154 annotated as H32 1 2?
Many thanks.
"Note that the figure showing the relationship between primitive
and R-centred rhomohedral cells with hexagonal axes is clickable
Rhombohedral with Hexagonal axes
146. /R/ 3 <http://img.chem.ucl.ac.uk/sgp/large/146bz1.htm> 148.
/R/ -3 <http://img.chem.ucl.ac.uk/sgp/large/148bz1.htm> 155.
/R/ 3 2 <http://img.chem.ucl.ac.uk/sgp/large/155bz1.htm> 160.
/R/ 3 /m/ <http://img.chem.ucl.ac.uk/sgp/large/160bz1.htm> 161.
/R/ 3 /c/ <http://img.chem.ucl.ac.uk/sgp/large/161bz1.htm> 166.
/R/ -3 /m/ <http://img.chem.ucl.ac.uk/sgp/large/166bz1.htm>
167. /R/ -3 /c/ <http://img.chem.ucl.ac.uk/sgp/large/167bz1.htm>
H-centred Trigonal
143. /H/ 3 <http://img.chem.ucl.ac.uk/sgp/large/143bz1.htm> 144.
/H/ 3_1 <http://img.chem.ucl.ac.uk/sgp/large/144bz1.htm> 145.
/H/ 3_2 <http://img.chem.ucl.ac.uk/sgp/large/145bz1.htm> 147.
/H/ -3 <http://img.chem.ucl.ac.uk/sgp/large/147bz1.htm> 149.
/H/ 3 2 1 <http://img.chem.ucl.ac.uk/sgp/large/149bz1.htm> 150.
/H/ 3 1 2 <http://img.chem.ucl.ac.uk/sgp/large/150bz1.htm>
151. /H/ 3_1 2 1 <http://img.chem.ucl.ac.uk/sgp/large/151bz1.htm>
152. /H/ 3_1 1 2
<http://img.chem.ucl.ac.uk/sgp/large/152bz1.htm> 153. /H/ 3_2 2
1 <http://img.chem.ucl.ac.uk/sgp/large/153bz1.htm> 154. /H/ 3_2
1 2 <http://img.chem.ucl.ac.uk/sgp/large/154bz1.htm> 156. /H/ 3
1 /m/ <http://img.chem.ucl.ac.uk/sgp/large/156bz1.htm> 157. /H/ 3
/m/ 1 <http://img.chem.ucl.ac.uk/sgp/large/157bz1.htm>
158. /H/ 3 1 /c/ <http://img.chem.ucl.ac.uk/sgp/large/158bz1.htm>
159. /H/ 3 /c/ 1 <http://img.chem.ucl.ac.uk/sgp/large/159bz1.htm>
162. /H/ -3 /m/ 1 <http://img.chem.ucl.ac.uk/sgp/large/162bz1.htm>
163. /H/ -3 /c/ 1
<http://img.chem.ucl.ac.uk/sgp/large/163cz1.htm> 164. /H/ -3 1
/m/ <http://img.chem.ucl.ac.uk/sgp/large/164bz1.htm> 165.
/H/ -3 1 /c/ <http://img.chem.ucl.ac.uk/sgp/large/165cz1.htm>
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