I was going to say that we could adopt the convention that the
default setting of a centrosymmetric space group is the one with the
origin on an inversion centre, since this is assumed by all programs
that I am aware of, thus making ':2' for 'second setting' unnecessary
and keeping the name to 11 characters. At first glance this would
solve the problem for Ian's two 'long' space groups ('P 42/n n m :2'
and 'I 41/a m d :2') since only the second of the two settings given
in volume A of International Tables has the origin on an inversion
centre. However as chance would have it, both these space groups have
another alternative non-equivalent setting that also has the origin
on an inversion centre but this third setting is not given in volume
A of the IT!
Perhaps I should mention that with the SHELX method of specifying
the space group symmetry using the symmetry operators, alternative
settings, specified in IT or not, cause no problems. But then we
would not have had this thread (or the H3/R3 and P21221 threads).
George
Prof. George M. Sheldrick FRS
Dept. Structural Chemistry,
University of Goettingen,
Tammannstr. 4,
D37077 Goettingen, Germany
Tel. +49-551-39-3021 or -3068
Fax. +49-551-39-22582
On Mon, 6 Sep 2010, Ian Tickle wrote:
> It seems that it's the new addition of ':n' which has pushed it over
> the limit of the 11 char field. Has this been thought through? I
> can see that the ':n' qualifier is necessary to disambiguate alternate
> origins. Without the redundant formatting spaces 9 chars would be
> sufficient even for 'P 42/n n m :2' which is indeed the longest one at
> 13 chars (also 'I 41/a m d :2').
>
> -- Ian
>
> On Mon, Sep 6, 2010 at 2:57 PM, Martyn Winn <martyn.w...@stfc.ac.uk> wrote:
> >> > There seem to be a few CCP4 Fortran files that have character spgnam*10
> >> > from the good old days ...
> >>
> >> What good old days were those? The Cryst1-format for PDB-files in the ccp4
> >> documentation says
> >> 56-66 Space group symbol, left justified (not used)
> >> which is eleven characters. Were there days when this was different?
> >>
> >> Tim
> >
> > <old_fogey>I remember when we didn't bother with spacegroup on the
> > CRYST1 line at all, let alone formatting it correctly.</old_fogey>
> >
> > And what about 'P 42/n n m :2' which is more than 11 characters?
> >
> > I realise my answer doesn't help with Coot problems, but I will clean up
> > CCP4 Fortran programs at least.
> >
> > m
> >
> > --
> > ***********************************************************************
> > * *
> > * Dr. Martyn Winn *
> > * *
> > * STFC Daresbury Laboratory, Daresbury, Warrington, WA4 4AD, U.K. *
> > * Tel: +44 1925 603455 E-mail: martyn.w...@stfc.ac.uk *
> > * Fax: +44 1925 603634 Skype name: martyn.winn *
> > * URL: http://www.ccp4.ac.uk/martyn/ *
> > ***********************************************************************
> >
>
>
