[Pw_forum] What happens at REALLY large ectuwfc?

[Stefano Baroni]

Lorenzo: your (ir-)rationale may be more or less justified for separable potentials, but it is certainly wrong for good ol' semilocal ones. SB

On Jan 24, 2010, at 9:05 PM, Lorenzo Paulatto wrote:

> I'm reposting here a message that I mistakenly sent privately to Brad:
> 
> have a look at the total-energy components: if the one-electron  
> contributions increases  at the expenses of the other terms (mostly  
> the hartree term) than you have found a ghost in the pseudopotential.  
> As far as I know, all non-local separable pseudopotentials have  ghost  
> states for large enough values of the curoff.
> 
> I'm not really sure my impression is correct, but I've always had  
> problems with large enough cutoffs with any pseudopotential I have  
> tried. My rationale is more or less on this line: the pseudopotential  
> only have Fourier components up to a certain threshold; plane waves  
> over that threshold do not feel any direct effect from the ions. As a  
> consequence this very high frequency plane waves gain nothing by  
> forming a charge density close to the ions, instead they can just  
> spread around to minimize the Hartree energy (which decreases) at the  
> expenses of kinetic energy (which increases).
> 
> cheers
> 
> 
> -- 
> Lorenzo Paulatto
> SISSA  &  DEMOCRITOS (Trieste)
> phone: +39 040 3787 511
> skype: paulatz
> www:   http://people.sissa.it/~paulatto/
> 
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Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
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