[Pw_forum] pbe with norm conserving pp convergence problem

[Jia Chen]

Dear Peng,

For AFM case, you can set tot_magentization = 0, for FM case, you need
to know tot_magnetization from experiments or previous calculations.
Or you can use the int(absolute magnetization) from you AFM
calculations.

Trying to converge total energy with respect to wave function cutoff
is usually not a good idea. If you just want to choose a good cutoff
energy for calculations, first thing you can do is to look into those
pseudopotentials you are using. If you can find recommended cutoffs,
you probably can just use the highest cutoffs in your system.

Bests
Jia

On Mon, Sep 10, 2012 at 5:02 PM, Peng Chen <pchen at ion.chem.utk.edu> wrote:
> Dear Dr.  Giannozzi,
>
> Thanks for your reply. I use smearing for computing the band structure in
> afm and fm states. It looks there is still a lot to learn. If I use
> occupation=fixed to calculate afm/fm states, shall I just set
> tot_magnetization=0 or 1?
>
> If I didn't set ecutrho, the default value of ecutrho is 4*ecutwfc. So the
> results are the same as the following, and the energy doesn't decrease
> monotonically. I tried to decrease degauss to 0.005 Ry, I got the similar
> results. What I can do to make the energy converge?
>
> ecutrho=4*ecutwfc
> ecutwfc     energy            total force
> 30 -1086.672528 1.335253
> 40 -1119.972723 0.690327
> 50 -1129.973333 0.690484
> 60 -1134.622157 0.640747
> 70 -1136.892534 0.617201
> 80 -1137.666471 0.616635
> 90 -1137.620919 0.610216
> 100 -1137.238099 0.615361
> 110 -1136.89911         0.62063
> 120 -1136.866006 0.622763
>
> On Mon, Sep 10, 2012 at 3:45 PM, Paolo Giannozzi <giannozz at democritos.it>
> wrote:
>>
>>
>> On Sep 10, 2012, at 16:35 , Peng Chen wrote:
>>
>> > I tried to calculate an insulator Ni3V2O3 using pbe norm conserving
>> > pp from pslibrary. But the energy related with ecutwfc is not
>> > converged. It reaches minimum at ecutwfc=80 Ry. But when I fix
>> > ecutrho=320 Ry and increase  ecutwfc, it starts to decrease
>> > monotonically. I am not sure if the system reaches the convergence
>> > at ecutwfc=80 Ry.
>> > (smearing=mv, Degauss=0.01 Ry and kpoints = 4 4 3)
>>
>> if it is an insulator, why are you using smearing? Apart from this:
>> with norm-conserving PP, ecutwfc is the only parameter defining
>> the basis set. You should not set ecutrho.
>>
>> P.
>> ---
>> Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
>> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>> Phone +39-0432-558216, fax +39-0432-558222
>>
>>
>>
>>
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>
>
>
>
> --
>   Best Regards.
>         Peng
>
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-- 
Jia Chen
webpage: www.princeton.edu/~jiachen