Haibei Huang haibeih at student.unimelb.edu.au
Mon Sep 1 04:53:00 CEST 2014

```Dear Axel,

I will try to understand and spent sometime learning what you suggested me
to do.

Best regards and have a good day!
Haibei

On Mon, Sep 1, 2014 at 11:41 AM, Axel Kohlmeyer <akohlmey at gmail.com> wrote:

>
> On Sep 1, 2014 1:16 AM, "Haibei Huang" <haibeih at student.unimelb.edu.au>
> wrote:
> >
> > Dear Axel,
> >
> >
> > The truth is that I was trying to diagonalize a matrix made of a serials
> of Energies obtained by pw.x, while some of elements in the matrix is quite
> small (e.g. 10^-7 or 10-^8). Thus, I would like to know how many digits I
> could trust in Energies. Or at least I should keep the Energies and these
> small elements in the same scale, say 10^-8.
>
> For that, you do _not_ need more digits for exactly the reason I gave you.
> If you output more digits, you are just adding random numbers. Literally.
>
> >
> > Please let me know if you or anyone know how to change the code showing
> more digits in pw.x.
>
> Many people know (including me). But why should anybody tell you, if what
>
> In general, please spent a little time learning about the systematic
> errors of DFT,  the numerical precision of floating point numbers, the
> accuracy of a self-consistent calculation and error propagation.
>
> You should quickly see the folly of your request.
>
> > Best regards
> > Haibei
> >
> >
> > On Sun, Aug 31, 2014 at 1:51 PM, Axel Kohlmeyer <akohlmey at gmail.com>
> wrote:
> >>
> >>
> >> On Aug 30, 2014 10:57 PM, "Haibei Huang" <
> haibeih at student.unimelb.edu.au> wrote:
> >> >
> >> > Dear All,
> >> >
> >> > I am aware of that the QE will only show at most 8 digits after the
> decimal point in the output file, while more digits are needed in my
> calculation.
> >> >
> >> > Could any of you provide a way to increase the number digits after
> the decimal point?
> >>
> >> What is the point of using more digits, when the error is larger? You
> could just add random digits and have the same effect.
> >>
> >> >
> >> > Thanks for your time!
> >> > Regards
> >> > Haibei
> >> >
> >> >
> >> > _______________________________________________
> >> > Pw_forum mailing list
> >> > Pw_forum at pwscf.org
> >> > http://pwscf.org/mailman/listinfo/pw_forum
> >>
> >>
> >> _______________________________________________
> >> Pw_forum mailing list
> >> Pw_forum at pwscf.org
> >> http://pwscf.org/mailman/listinfo/pw_forum
> >
> >
> >
> > _______________________________________________
> > Pw_forum mailing list
> > Pw_forum at pwscf.org
> > http://pwscf.org/mailman/listinfo/pw_forum
>
> _______________________________________________
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> Pw_forum at pwscf.org
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>
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