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

[Stefano de Gironcoli]

On 04/20/2011 05:46 PM, Paolo Giannozzi wrote:
> On Apr 20, 2011, at 16:02 , Eduardo Ariel Menendez Proupin wrote:
>
>> I am not sure if the calculation is still variational with
>> ultrasoft pseudopotentials
> it should be
>
>> or even if the Hohenberg-Kohn lemma is valid with non local
>> pseudopotentials
> there is some old work by Gilbert on this subject: http://prb.aps.org/
> abstract/PRB/v12/i6/p2111_1
>
>> With QE I have always seen the energy to decrease when the cutoffs are
>> increased, but with VASP, I always see an oscillation in the total
>> energy
>> when the cutoff is incremented.
> just guessing: it might be a consequence of real-space treatment of
> augmentation
> functions.

actually it can happen for US pseudo, if the cutoff for the density is 
not large enough, that the energy increases with increasing cutoff.. 
just because the augmentation charges are not integrated correctly and 
the error can have any sign. If ecutrho is sufficient to integrate 
correctly augmentation charges the energy should be variational w.r.t. 
ecutwfc .

stefano



> 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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