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["Nuno A. G. Bandeira" <nuno.bandeira@ist.utl.pt>]

Xiulin Ruan wrote:
> Dear Nuno,
>
> Thanks for your inspiring discussions, see my comments below.

You're welcome Xiulin.

> We have done the cluster calculations and we like the results. Here we are
> just trying to find out the possibilities of improving our calculations. As
> you said, the effects of different hosts on the energy levels can be
> addressed by using a larger cluster, by filling the first coordination
> sphere of the TiO6 octahedron with Al or Y atoms. But we will still have a
> problem in studying the electron-phonon coupling in the nonradiative decay
> process. We did it using the cluster model and the work was accepted for
> publication, but the criticism from a referee still remains that we were
> dealing with molecular vibrations, not really lattice phonons. In fact we
> are not so satisfied ourselves to simulate the electron-vibration coupling
> of the Ti doped cluster but claim it to be the electron-phonon coupling of
> Ti doped solids. 

Could the referee have done any better ? I think you've reached a 
technical limit in my opinion, whichever way you look at it.

> > So if you fill the first coordination sphere of the TiO6 octahedron with
> > Al atoms as a first approximation it would still be ridiculous to claim
> > that Ti is an impurity.
>
> In view of the concentration, wouldn't the cluster model have a sort of
> "higher concentration" since it has a smaller size?

No matter how you create the model it will always be high in 
concentration. Typically you're talking about a small percentage in the 
real crystal so you should have one TiO6 unit for many dozens or 
hundreds of AlO6 octahedra. So if you create a unit cell it will have to 
be really big with lots of atoms and the same is true for your finite 
cluster.

The only other approach that I can see you could try using is the 
embedded cluster technique which is present in MOLCAS. You create an 
artificial potential to simulate the presence of the crystal and compute 
vibrational couplings from it. It would still be a molecule though.


--
Nuno A. G. Bandeira, AMRSC
Graduate researcher and molecular sculptor
Inorganic and Theoretical Chemistry Group,
Faculty of Science
University of Lisbon - C8 building, Campo Grande,
1749-016 Lisbon,Portugal
http://cqb.fc.ul.pt/intheochem/nuno.html
Doctoral student @ IST,Lisbon
--