[Pw_forum] new bfgs: strange behavior doing vc-relax

[Максим Попов]

Dear Stefano de Gironcoli,

2011/4/19 Stefano de Gironcoli <degironc at sissa.it>

>      have you bothered looking at the output ? has the bfgs procedure
> converged ?
>

Yes, I have looked. If you look carefully at one of the previous posts,
you'll see
that bfgs procedure converged.


>      Notice that in recent versions of vcrelax one additional scf
> calculation is performed at the final configuration reinitializing
> reciprocal lattice vectors .
>

This has been already explained by Dr. Giannozzi in previous posts too.


>      this has nothing to do with the bfgs procedure. it's a check to
> verify what is the impact of the deformation of the cutoff "sphere"
> induced by the cell-shape change.
>

My question is exactly about this. More specific: why deformed cutoff
"sphere" gives lower total energy compared to undeformed one?



>    if the cutoff is large enough the change should be very small. 0.5
> mRy looks small to me.
>

Is there any criteria for an energy difference to be called "small"?

-- 
Best regards, Max Popov
Ph.D. student
Materials center Leoben (MCL), Leoben, Austria.
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