[Pw_forum] "charge is wrong" error in semiconductor slab calculation

[J. J. Ramsey]

----- Original Message ----

> From: Eyvaz Isaev <eyvaz_isaev at yahoo.com>
> To: J. J. Ramsey <jjr19 at uakron.edu>; pw_forum at pwscf.org
> Sent: Tuesday, December 2, 2008 3:47:11 PM
> Subject: Re: [Pw_forum] "charge is wrong" error in semiconductor slab calculation
> 
> Hi, 
> 
> I will try to repeat my own reply as it was sent only to the first address. That 
> seems to be quite strange, because I used "Reply".
> 
> >     ibrav = 8,
> >     a = 3.92232131524178,
> >     b = 3.92232131524178,
> >     c = 22.207375,
> 
> Why you use orthorhombic lattice instead of simple tetragonal (ibrav=6) as a=b?

I'll probably need to change my input file anyway to account for surface reconstructions, and in that case a probably won't equal b. It just makes the input file easier to tweak in the future.

> This problem was discussed before many times (you could search in the forum 
> archive):

I did search in the archive, but there were several answers, including possible faults in the geometry. I was a bit uncertain about which of them applied to me.

> So, you should include "occupations" and related keywords, otherwise you have a 
> semiconducting system that causes the charge deficiency due to insufficient 
> bands number.

I used these options:

    occupations = 'smearing',
    degauss = 0.05D0,

This seems to have worked.

> Please, provide your affiliation, too.

University of Akron. Oddly enough, I'm in the Civil Engineering Department, but I and the group of students with which I work are studying quantum dots and their growth.