[Pw_forum] How to set ecutwfc and ecutrho

[xirainbow]

Dear Li：


I am curious about the calculation speed related to "ecutwfc" and "ecutrho".
> As indicated in the tutorial, ecutwfc represents the energy cutoff (Ry) and
> ecutrho refers to kinetic energy cutoff for charge density and potential. I
> cannot fully understand the meaning of that brief description.

If you use Norm-concerving PP, you can just omit the parameter "ecutrho".
If you use Ultra-soft PP, you must set "ecutrho" as (8~12)X"ecutwfc".
You will fully understand the "ecutrho" after reading some paper about
Ultra-soft PP：）  (For example：PRB, 41 7892)



> From my experience (vasp), the larger the energy cutoff, the slower the
> calculation would be, but more accurate.

Yes， it is true for PWscf, too.

I just would like to know how to set the experience values of the two flags
> for the case of metal bulk (and surface) and metal oxide bulk (and surface)?
> Thank you.
>
I think,  the value is different with different kind of  metal.
You can take a convergence test to get proper "ecutrho" and "ecutwfc" ：）

____________________________________
Hui Wang
School of physics, Nankai University, Tianjin, China
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