[Pw_forum] graphene on BN calculation

[mohamed sabri majdoub]

Thank you a lot Mr Lorenzo for your suggestions.
I will try them and thank you again for your help.

Regards,

On Wed, Dec 16, 2009 at 11:22 AM, Lorenzo Paulatto <paulatto at sissa.it>wrote:

> Replying to message "[Pw_forum] graphene on BN calculation" from mohamed
> sabri majdoub (16/12/09):
>
> > I am not sure that I am doing it the right way. I am using 40 processors
> > and I the calculations look very slow to me.
>
> Well, it's a big system. You can speed it up by using tqr=.true.
> (real-space augmentation charge). There is also an experimental real-space
> algorithm, but I don't know how reliable it is at the moment (you can
> contact baris _at_ sissa.it for additional info).
>
> >           tstress  = .t.
>
> there is no need to print the stress, and it takes time to compute (not
> much)
>
> >     diagonalization = 'cg'
>
> For better performance you should use the default (david). If you have
> some problem with it, you should ask for help on the forum before falling
> back to cg, which is non much more robust and quite a bit slower. Also,
> diagonalization errors are most of the time input errors/bad atomic
> positions.
>
>
> > K_POINTS automatic
> > 30 30 1 1 1 0
>
> this is a huge number of k-points for such a cell, are you sure you need
> all of them? Remember that every time you increase the cell size by N you
> can reduce the number of k-points by the same factor. (e.g. a 2x2x2
> super-cell only need on eighth of the k-points of the original cell).
> Computation time scales linearly with the number of points, e.g. "10 10 1
> 1 1 0" will be about 9 times faster.
>
> best regards
>
>
> --
> Lorenzo Paulatto
> SISSA  &  DEMOCRITOS (Trieste)
> phone: +39 040 3787 511
> skype: paulatz
> www:   http://people.sissa.it/~paulatto/<http://people.sissa.it/%7Epaulatto/>
>
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