# [Pw_forum] ecut vs energy

Giovani Faccin faccin.giovani at gmail.com
Tue Jun 14 20:39:26 CEST 2011

```Dear Amin,

1 - Convergence should not depend on the structure. You can check it for any
reasonable structure (obviously if you push two atoms inside each other
you'll be forcing your pseudopotential reliability, but for normal, not
optimized structures, with reasonably low forces, should work fine).

2 - Your energy convergence table looks normal to me. The question you
should now ask is: for the purpose you are doing your calculation, how much
precision do you need? Is it 10^-1, 10^-2, 10^-3 Ry? That answer will define
the value of ecut you have to use.

Best,

Giovani M. Faccin
UFMS/Unicamp - Brazil

2011/6/14 Amin Torabi <amin.torabi at gmail.com>

> Dear experts!
>
> Could you please have a look at my input file, attached to this email.
>
> My main problem is that I expect the total energy to converge at lower
> ecutwfc energy. ( or I am expecting too much?)
>
> ecut    energy
> 25     -38.36026321
> 30     -38.44145201
> 35     -38.49537648
> 40     -38.53312799
> 45     -38.55904483
> 50     -38.57650475
> 55     -38.58840904
> 60     -38.59670631
> 65     -38.60253103
> 70     -38.60653038
> 75     -38.60918176
> 80     -38.61090436
> 85     -38.61200805
> 90     -38.61269007
> 95     -38.61308582
> 100    -38.61329742
>
>
>
> Notes:
>
> 1. Do I have to be at the minimum structure to check for convergence of
> ecut vs energy, or I can check the convergency from a non-optimized
> structure?
>
> 2. I used USPP for one of my atoms and NCPP for the other atom, and set
> ecutrho = 10*ecutwfc...
>
>
>
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>
>

--
Giovani
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20110614/8bb3e186/attachment.html>
```