[Pw_forum] Fluorine and PBE PAW/US

[Thomas Brumme]

Dear Benjamin Smith,

what do you mean with convergence graph? The total energy with 
increasing cutoff?
I thought that this does not tell you anything, but maybe I'm wrong. You 
should look
at changes in the electronic structure and geometry...

Furthermore,
1. if you want to calculate a molecule, why do you use more k points 
than just Gamma?
2. a box of a size of about 5 Angstrom might be too small (celldm is in 
Bohr)

I guess that the box size together with the two points above can lead to 
a minimum in the
total energy which has nothing to do with the molecule. Easy way to test 
would be to
increase the box.

Regards

Thomas

On 09/15/2014 11:41 AM, Benjamin Smith wrote:
> Hello,
>
> I have been running tests of PBE pseudopotentials using an F2 molecule 
> within a cubic box.  For pbe-n-kjpaw, pbe-n-rrkjus and both of their 
> relativistic equivalents, the convergence graph is very strange.  
> There is not a smooth decline in the graph, it actually dips to a 
> minimum around 35Ry, and does not satisfactorily converge until around 
> 70Ry.  I have not seen a graph such as this for convergence before, 
> any advice would be appreciated.
>
> Here is my input:
>
> &control
>     prefix='testf',
>     pseudo_dir='/home/chemeng/Benjamin/ppots'
>     outdir = '/home/chemeng/Benjamin/PVDF/test',
>  /
>  &system
>     ibrav= 1, celldm(1) =10, nat=2, ntyp= 1,
>  ecutwfc = 100 ,
>  /
>  &electrons
>  /
>  /
> ATOMIC_SPECIES
> F 18.998 F.pbe-n-rrkjus_psl.0.1.UPF
> ATOMIC_POSITIONS (crystal)
> F        0.000000000  0.00000000   0.000000000
> F        0.0 0.0 0.268
> K_POINTS automatic
> 4 4 4 0 0 0
>
>
> Thanks.
>
> Benjamin Smith
> Visiting Researcher
> Chemical and Process Eng.
> Uni. of Strathclyde
>
>
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-- 
Dr. rer. nat. Thomas Brumme
Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie
Sorbonne Universités - UPMC Univ Paris 06
4 Place Jussieu
75005 Paris

Tel:  +33 (0) 1 442 77204

email: Thomas.Brumme at impmc.upmc.fr

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