[Octopus-users] Phosphorescence

[Miguel Marques]

  Hi,

> I am Jose Gracia and I hope a new user of OCTOPUS, we would
> like to start a theoretical study of the phosphorescence of a crystal
> and we are thinking into use OCTOPUS, but we have some questions that
> may it is best to ask people with some experience:
> 
> - First we would like to include periodic conditions in our
> calculations, but if this is not possible we can use a cluster model.

It is possible, to some extent, to study extended systems with octopus.
However, the code is not thoroughly tested, so I would not recommend it
to do response calculations for solids.

> - Second we are talking about a big system with 160 atoms in the unit cell.

Well, 160 atoms is not that large ;) It depends on what you want to do
with it. The proteins I normally run have around 100 atoms and I can
manage to calculate them in a cluster of PIVs ;)

> We know that it is a difficult problem, this is because we are looking
> for the best code possible. If you think that OCTOPUS it is not the
> best option and you have any other idea, we really appreciate any
> idea.

  Well, for your particular problem I would not really recommend
octopus. You want to calculate a periodic system (a cluster model with a
couple of unit cells will probably be quite large I guess), and octopus,
for the moment, is more adequate for finite systems. Furthermore (and I
guess your system is a semiconductor) you should be aware of the
difficulties of DFT in handling the electronic excitations in such
systems. Normally one has to do GW and sometimes Bethe-Saltpeter to get
good spectra. So, maybe you should seek help of guys more used to
periodic systems. I can name Andrea Marini in Rome or Valerio Olevano
who is now in Grenoble.

  I don't know if I helped. In any case, if you have some more doubts
you can write me again ;)
  miguel