[CPMD-list] problems with point group recognition and symmetrisation of coordinates

[Juerg Hutter]

Hi

> Hello,
>
> On Fri, Mar 19, 2004 at 01:55:01PM +0100, Juerg Hutter wrote:
> > C   - Positioning of the molecule:
> > C            z-axis   is the principal axis
> > C            x-axis   is the two-fold axis
> > C            xz-plane is the sigma-v plane
> > C            xy-plane is the sigma-h or the Cs symmetry plane
> > C            origin   is the center of inversion

These rules are of course only to be applied if possible, with the
first one having highest priority.

>
> These conditions cannot be fulfilled completely in the case of the Td-group.
> Here the three C2-axes are orthogonal to each other, and the (four) principal
> axes (C3) are not orthogonal to any of the C2-axes.
> For some reason, however, using one of my two examples (the one with the z-axis
> corresponding to a C2-axis and the xz-plane as a mirror-plane, see previous
> posting), the point group Td was recognised, but, the symmetrisation failed.
>
> Some years ago I used CPMD 3.0h (!) for a molecule in C3v-symmetry, at that
> time the symmetrisation worked well (at least for this case of C3v). Using
> the same input and CPMD 3.7.2 the symmetrisation fails. This might be an
> indication that at least the problem of the symmetrisation of coordinates
> could be related to a bug which might have arisen in the development towards
> version 3.7.2.

Between these two versions the symmetry code for crystal groups has
been implemented. There were some problems with the molecular
points groups after that.

>
> > It's still possible that there are some bugs for certain
> > point groups.
>
> Yes, e.g. systems in D3d are not recognised as such. I carefully tested
> it according to the rules you mentioned. At least C3v was working here,
> maybe the problems are connected to the three C2-axes in the xy-plane.
>
> Is there a chance that these problems might get fixed in the next CPMD release?

Unfortunately not.

regards

Juerg Hutter



>
> With best regards,
> Christian Tuma.
>
> --
> Christian Tuma             Humboldt-Universitaet Berlin
> ct at chemie.hu-berlin.de     Arbeitsgruppe Quantenchemie (Prof. Sauer)
> phone: +49-30-20937140     Brook-Taylor-Str. 2, 12489 Berlin, GERMANY
> fax:   +49-30-20937136     http://www.chemie.hu-berlin.de/ag_sauer
> _______________________________________________
> CPMD-list mailing list
> CPMD-list at cpmd.org
> http://www.cpmd.org/mailman/listinfo/cpmd-list
>