[Pw_forum] electron phonon coupling of supercells

[Nicola Marzari]

>       I encounter difficulty in performing electron-phonon
> coupling (EPC) on a supercell. Take NaCl as a example,
>  I construct a 2*2*2 supercell in the unit of the NaCl primitive
>  cell, which has 16 atoms. But the supercell has a P1 space
> group. We all kown that the EPC is very time-consuming. Time to
> perform a EPC on such a supercell will be unbearable. What can
>  I do to handle such a problem?

Use the unit cell instead ? If you need the supercell, then there
is no easy solution (apart from the ones gone below).

>      My second question is how much the k-mesh should choose
>  for such a supercell when do the EPC calculation ? Could someone
>  give some empirical advice ?

1) Start with a coarse sampling, and increase until it is converged.

2) Use Wannier functions as an interpolator:

http://arxiv.org/abs/cond-mat/0507089 (also available in PRL) and
especially http://arxiv.org/abs/cond-mat/0608257. There is more
very pretty but yet unpublished work from the Berkeley group - wait
a little for that to appear.


				nicola

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Prof Nicola Marzari   Department of Materials Science and Engineering
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