[QE-users] Problem for testing k convergence

[Pietro Delugas]

Hello

it seems fine; you are almost at convergence.

If I understand your doubt, you are confusing with the convergence in 
cut-off energy.

At variance with convergence for the plane wave basis set, the 
convergence in the k-points mesh is not "variational". It is not that a 
denser mesh has to give you a lower or equal value of the energy, you 
are just removing erroneous contribution to the sum in the Brillouin 
zone coming from oscillating terms of shorter and shorter periodicity. 
Removing more terms should eventually give you a more precise estimate 
of the integral.

What you have to minimize is the difference of the energy at a certain 
mesh density with the ones  obtained using  denser meshes, an that 
difference in your case is indeed decreasing

I hope it helps.

regards

Pietro

On 01/10/20 07:20, Anupriya Nyayban wrote:
> Dear experts/users,
>
>
> I was trying to check the convergence for an orthorohmbic system and 
> got ecut convergence for 70. Later, I choose a smaller ecut of 40 for 
> testing kmesh convergence to reduce the computation time. But, I 
> observed a opposite pattern of convergence graph which is attached 
> below. Please suggest me what could be the possible reason! ( I choose 
> the key 'K_POINTS (automatic)' as ' $CUTOFF $CUTOFF $CUTOFF 1 1 1', 
> where CUTOFF value varies from 3 to 7.)
>
> Any kind suggestions will be helpful for me.
>
>
> Thank you
>
> With regards
> Anupriya Nyayban
>
>
>
>
>
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