[Pw_forum] problem with supercell

[Giuseppe Mattioli]

Dear Halima

As I wrote some days ago, 1,24 or 1.24 does not make any difference.  
Your structure is NOT wurtzite GaN at all... Check the right wurtzite  
structure, for example here (you may use "Vesta", or even "Avogadro"  
to open the .cif files).

http://www.crystallography.net/

lda_plus_u=.true.  Hubbard_U(1)=8, Hubbard_U(3)=4.5,

It may be a good choice, but you have got only two species, not three,  
and you do not need nspin=2.

   ecutwfc = 30.0, ecutrho = 120,

As pointed out by Lorenzo, you should use ecutrho=8~10*ecutwfc

HTH

Giuseppe


Quoting Lorenzo Paulatto <lorenzo.paulatto at impmc.upmc.fr>:

> On 11/03/2013 07:18 PM, Halima Zaari wrote:
>> dear quantum espresso users
>> i tried to do input of GaN supercell with 56 atom
>> I plots the dos of GaN it gives me mttalic behavior while in the
>> literature is semiconductor.
>
> Dear Halima,
> in your input you write:
>  ibrav=4,celldm(1)=12.06,celldm(3)=1,24,nat=56, ntyp=2,
>
> note that 1,24 is different from 1.24 : it will make your cell too small
> which can cause a system to become metallic.
>
> I also noted that your value of ecutrho may be too low, as it is only
> 4*ecutwfc and you are usng ultrasoft (note van=Vanderbilt) pseudopotentials.
>
> Finally, I do not understand what you're doing with the magnetization
> and Hubbard U, but I'm don't know that method very well, hence I'll
> leave any comment to more expert people.
>
> good work!
>
>
> --
> Dr. Lorenzo Paulatto
> IdR @ IMPMC -- CNRS & Université Paris 6
> phone:+33 (0)1 44275 084 / skype: paulatz
> www:  http://www-int.impmc.upmc.fr/~paulatto/
> mail: 23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 5
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