[Pw_forum] test case with structure relaxation

[Wei Lai]

Dear Giuseppe,

I tried ecutrho as 8 or 12 times of ecutwfc=30 for ultrasoft PP. Also tried
norm conserving PP with ecutwfc=70 and ecutrho=280. The c/a ratio is still
far off from the expected 1.4142. Very confused.

Regards, Wei
Wei Lai
Michigan State University
East Lansing, MI 48824

On Wed, Mar 28, 2012 at 10:43 AM, Giuseppe Mattioli <
giuseppe.mattioli at ism.cnr.it> wrote:

>
> Dear Wei
>
>
> >  &system
> >     ibrav=  7, celldm(1) = 5.6298, celldm(3) = 1.4, nat=  2, ntyp= 2,
> >     ecutwfc =30, input_dft='pw91'
> >  /
>
> >  ATOMIC_SPECIES
> >  Mg  24.305 Mg.pw91-np-van.UPF
> >  O   15.999 O.pw91-van_ak.UPF
>
> You are using ultrasoft pseudopotentials. You should explicitly assign a
> value to the ecutrho
> parameter (&system list). The default value is 4*ecutwfc, and it is a good
> value for norm conserving
> PPs. A 6*ecutwfc~10*ecutwfc value is considered as a safe~good one in the
> case of ultrasoft PPs
>
> HTH
>
> Giuseppe
>
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>   Giuseppe Mattioli
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