[CPMD-list] Band gap and hybride EXC

[Juerg Hutter]

Hi

> Dear users,
>
> Is there any recipie to calculate band gap for
> semiconductors, say for Si, using hybride EXC (ACM0,
> ACM1, etc.)? Should I first calculate optimized
> wavefunctions and then start for EXC calculations?
> Should wavefunction optimization be carried out using
> just the LDA functional?

The hybrid functionals have to be applied in a self-consistent
calculation as any other functionals. Starting with optimized
wavefunctions (from another functional) might help to reduce the
number of iterations needed but is not essential for the
calculation otherwise.

Some words of caution:
- hybrid functionals are not implemented with k-points
- there is a problem with a divergence for periodic boundary
  conditions. The standard way of dealing with this is by adding
  an integrable compensation charge. This is not implemented in
  CPMD. The only way to handle PBC at the moment is by using
  screened exchange. This will change the functional and has to
  be tested case by case.

regards

Juerg Hutter


>
> Any hint will be appreciated.
>
> Bests,
> Eyvaz.
>
>
>
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