Scott: These are just the kind of problems I was having but I would add that for someone who is not savvy about crystallography, having to fake a crystal with a low symmetry space group is not terribly intuitive. I agree with you also about the symmetry of the neighbors but, again, i think that the benefit of an intuitive interface to what the scientist wants to do is a good thing. I think that having to use work-arounds is difficult to explain to new users. Perhaps a new chemistry student knows that his/her atom has an octahedral coordination. It woujld be good to be able to intuitively model that. Just my $0.02 Carlo On Wed, 5 Jan 2005 scalvin@slc.edu wrote:
Hi Carlo,
Hmmm...my initial reaction was that, rather than loading Artemis with a new option, it's better just to "fake it" by using a low-symmetry space group with a large lattice parameter and then truncating the cluster size at smaller than the unit cell. But I just tried this, and discovered an interesting problem, which you may have come across as well.
What I did was attempted to create an octahedral cluster by using a space group of P m 3 m (simple cubic) with a=10, an Fe at 0 0 0 absorbing, and an oxygen at 0.2 0 0 (thus an Fe-O distance of 2 angstroms). The cluster size is set at 5. As expected, that generates an octahedral cluster of oxygens around the Fe as a FEFF.INP file. But here's the problem: Artemis includes a potential for scattering atoms of Fe, and there aren't any in the list. FEFF, in turn, doesn't like that and won't run, causing Artemis to give the error message:
-- Carlo U. Segre -- Professor of Physics Associate Dean for Special Projects, Graduate College Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 Carlo.Segre@iit.edu http://www.iit.edu/~segre