[Pw_forum] Total energy does not coverge with ecut

[prasenjit.jnc at gmail.com]

Sometimes it is also difficult to converge the total energy. So usually it  
is better to check the convergence of the quantity you are interested in.

But anyway it is really strange that total energy doesn't converge at such  
abnormally high cut off values.

Did you test the pseudopotentials individually?? For eg. did you try  
calculating the bond lengths of say a nitrogen molecule & see how the  
results are??

With regards,

Prasenjit.

On Nov 6, 2008 5:45pm, Timothy Mason <thmason24 at yahoo.com> wrote:
> Dear Lorenzo,
>
> here are results for the lower energy range. Still doesn't seem to be  
converging.
>
> ecut energy energy differnce
> 30 -48.19258627
> 35 -48.19503183 0.00244556
> 40 -48.197306 0.00227417
> 45 -48.20217820 0.0048722
>
> thanks
>
> --- On Thu, 11/6/08, Lorenzo Paulatto paulatto at sissa.it> wrote:
> From: Lorenzo Paulatto paulatto at sissa.it>
> Subject: Re: [Pw_forum] Total energy does not coverge with ecut
> To: thmason24 at yahoo.com, "PWSCF Forum" pw_forum at pwscf.org>
> Date: Thursday, November 6, 2008, 10:08 AM
>
> Timothy Mason ha scritto:
> >
> > Gentlemen,
> >
> > My structures do not see to be converging with increased ecutwfc.
> > I'm setting ecutrho to ecutwfc * 12 and using US PP. below is a
> > table of ecut values vs energies vs difference from previous steps
> > followed by my input file followed by part of the output file. It
> > appears to begin to converge and 120 ecut but then jumps at 130 and
> > then more at 140.
> >
> Dear Timothy,
> these are ridiculous cutoff energy for ultrasoft pseudopotentials - they
> are very high for norm-conserving too! I suspect the presence of a
> high-energy ghost-state in one of the pseudopotential; these kind
> of
> states aren't usually harmful but can suddenly pop-up under some
> specifics conditions like high pressure or very high cutoff.
>
> What is happening when you try some reasonable cutoff in the 20-50 Ry  
range?
>
> regards
>
> --
> Lorenzo Paulatto
> SISSA & DEMOCRITOS (Trieste)
> phone: +39 040 3787 511
> skype: paulatz
> www: http://people.sissa.it/~paulatto/
>
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>
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