[Pw_forum] Improve convergence, slab and electric field.

[Tone Kokalj]

On Fri, 2010-08-27 at 10:29 -0500, joaquin peralta wrote:
> Dear pw_forum
> 
> I try to simulate a metallic slab under a electric field. In order to
> improve the convergence, I checked this web page :


>    edir                  = 3
>    emaxpos               = 0.9
>    eopreg                = 0.2
>    eamp                  = 0.019447
> /

This input explains why you face SCF problems: they are inevitable with
your dipole-layer specification. You have placed your dipole layer
from 0.9 to 0.9+0.2=1.1. Note that position of emaxpos/eopreg is in
internal units, in range [0,1].

This implies that you put your dipole layer starting near the bottom of
the slab and ending in the slab.

!!! The dipole-layer (i.e. region where the sawlike potential decreases)
should be located in the middle of vacuum layer. !!!