> it could happen that the coordinates you got from the database
> refer to a different origin...

Databases simply store the results of earlier determinations, for which
the symmetry setting and coordinates should be coherent. It is not unknown
for errors to occur, but commercial small structure databases ICSD and CSD
are carefully checked, as are CIFs published in journals such as Acta
Cryst.

The easiest and most powerful check for a fundamental error in the
structure description is to actually draw it on your computer - most
mistakes, such as wrong origin, will be immediately apparent. Both ICSD
and CSD allow you to draw structures. That's the first thing to do.

BTW ICSD-Web http://icsdweb.fiz-karlsruhe.de/ will now draw anisotropic
vibration amplitudes (also coming soon to Acta Cryst on-line). This is a
good test for systematic errors in data and structure refinements, as is
the calculation of bond-lengths and angles.

Alan
______________________________________________
Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
<[EMAIL PROTECTED]> +33.476.98.41.68
      http://www.NeutronOptics.com/hewat
______________________________________________

Reply via email to