[Pw_forum] optimal alpha not found

[Eyvaz Isaev]

Dear Paolo,

Thanks for correction.

Bests,
Eyvaz.
--- Paolo Giannozzi <giannozz at nest.sns.it> wrote:
> On Thursday 05 May 2005 17:43, Eyvaz Isaev wrote:
> 
> > Actually, the error means that the Ewald sum
> (ion-ion
> > energy contribution) could not converge for some
> > reason. I have to remind that the Ewald sum
> consists 
> > of two parts: erf(\alpha R)/R and erfc(\alpha
> R)/R.
> > The first term has a fast convergence in G-space,
> > while  the second term converges in R-space.
> > There are also 2 \alpha-dependent contributions,
> > excluded from sums.
> > Optimum \alpha has to be chosen so that it gives
> good
> > convergence for both G-, and R- sums.
> 
> the exact meaning of the error is that the code
> (PW/ewald.f90)
> could not determine a value for alpha giving a
> converged 
> G-space sum for the available set of G-vectors.
> "Optimal"
> is somewhat misleading in this respect. The only
> reasons
> for such error I can think of, iare either a very
> weird structure,
> or an exceedingly low cutoff
> 
> Paolo
> 
> -- 
> Paolo Giannozzi             e-mail: 
> giannozz at nest.sns.it
> Scuola Normale Superiore    Phone:   +39/050-509876,
> Fax:-563513 
> Piazza dei Cavalieri 7      I-56126 Pisa, Italy
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