[Pw_forum] accuracy of the energies printed to file

[Axel Kohlmeyer]

On Sat, Jan 30, 2016 at 3:38 PM, Małgorzata Wawrzyniak-Adamczewska
<mwaw at amu.edu.pl> wrote:
> Hello Stefano,
>
>
>
> the problem is that i would like to study the band structure etc. around the
> K point in graphene and graphene with adatoms with SO. With the accuracy of
> order 10^-4  I think I will not be able to see some important details.

on the other hand, i think it would be very advisable to do some
sensitivity analysis with respect to what level of systematic and
numerical accuracy is possible for the eigenvalue spectrum. chances
are, that you may just be digging around in numerical noise or that
any systematic differences may due to technicalities and not the
underlying physics. i.e. (small) changes to cutoffs, grids, number of
atoms, type of pseudopotentials, number of processors may cause
changes of equal or greater magnitude and thus would then render
findings questionable (to put it mildly).

axel.


>
> Best wishes,
>
>
>
> Malgorzata Wawrzyniak-Adamczewska
>
> Adam Mickiewicz University, Poznan, Poland
>
>
>
>  Message: 2 Date: Fri, 29 Jan 2016 14:13:33 +0100 From: stefano de gironcoli
> <degironc at sissa.it> Subject: Re: [Pw_forum] accuracy of the energies printed
> to file To: pw_forum at pwscf.org Message-ID: <56AB657D.9000704 at sissa.it>
> Content-Type: text/plain; charset="utf-8" do you really need to print the
> eigenvalues with 10^-7 eV accuracy ? stefano On 29/01/2016 14:08, Ma?gorzata
> Wawrzyniak-Adamczewska wrote:
>
> Dear QE users and developers, I was wondering if there is a possibility to
> increase the accuracy of the energies printed in the e.g. scf.out file or
> bands.out file? I find the accuracy of D^-4:
> -------------------------------------------------------------------------------------------------------
> k = 0.0000 0.0000 0.0000 ( 2289 PWs) bands (ev): -21.2789 -21.2789 -9.3618
> -9.3618 -4.7450 -4.7450 -4.7357 -4.7357 1.2876 1.2876 2.0573 2.0573 2.2604
> 2.2604 4.3273 4.3273 4.9921 4.9921 6.6656 6.6656 6.6734 6.6734 8.2476 8.2476
> 9.4082 9.4082 9.8358 9.8358 10.9914 10.9914 13.5952 13.5952
> -----------------------------------------------------------------------------------------------------
> and would like to increase it to D^-7. Thank you in advance, Malgorzata
> Wawrzyniak
>
>
>
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-- 
Dr. Axel Kohlmeyer  akohlmey at gmail.com  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.