[CPMD-list] multiplicity

[Ari.P.Seitsonen at iki.fi]

Dear Yixuan Wang,

> If the periodic boundary condition is applied to an isolated cluster system
> with spin=1/2 (multiplicity=2), should we still use the same multiplicity or
> we need other macroscopic information to determine it?
> 
> Additionally, if multiplicity=2 is specified for spin=1/2 system  in an
> input LSD approximation has to be added, however if multiplicity is absent (
> since default multiplicity is the smallest possible one, it should also be 2
> for odd electron system ), LSD is not necessary, which is much faster than
> the former. The question is if the latter is reliable. I appreciate your
> comments.

Sorry, I didn't quite get your question: Do you still want to simulate
the system as an isolated cluster, or a crystal?

  In the first case you should always use LSD, otherwise you will get
unphysical results.

  In the latter case it depends on the system you are studying; also
please be careful that your system is large enough in order to justify
using the Gamma point only. Is the band structure of the extended
system known? Since your system is radical your molecules might
dimerise etc in order to get rid off the unpaired electron. (Just a
thought, I'm not a chemist :v)

    Greetings,

       apsi

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