[Pw_forum] missing q point

[Gabriele Sclauzero]

Mehrnaz Anvari wrote:
> Dear Gabriele
> I compeletly agree with you. I work on graphene and it seems that it is 
> not necessary to use 2 2 2/4 4 4 grid. I just used them to see that as 
> Eyvaz suggested my error would be diappeared or not. Now I don't have 
> any problem with espresso-4.0.5 & thanks a lot because of your help. I 
> have another question when I use  c.blyp-mt.UPF pseudopotential and then 
> calculate frequency in gamma point, my optical frequency is about 
> 3400cm-1 but when I use 2 2 1 grid I gain 1528cm-1. I couldn't 
> understand the reason of it

Your question is not much clear too me.
Do you mean that the frequency obtained for the same q vector (0,0,0 in this case) is 
different if you perform a single q-point calculation w.r.t the frequency obtained when 
that q-point is included in a q-point grid (like the 221 you mention). This seems quite 
improbable to me.
Or maybe you mean that when computing dispersions from the 221 grid using Fourier 
interpolation the result is not good at Gamma? This may be since you are using a very 
small grid (try to check convergence by increasing the size of the grid).
Then there are many other convergence issues about cut-offs, k-point grids, PPs, ...

GS



>   Best Regards
> Mehrnaz
> Iran University Of science & Technology   
> 
>  
> 
> 
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