[Q-e-developers] problem with pressure calculation -- cp.x (bug?)

[Paolo Giannozzi]

I think I did the vdW-df porting to CP. I am quite confident that the
fixed-cell case works properly (if not, I must expunge a paper from my list
of publications!). The variable-cell case may have received no seriously
testing, though. I'll have a look sooner or later. If later, I'll disable
that case.

Paolo

On Tue, Sep 13, 2016 at 8:52 AM, Filippo SPIGA <
filippo.spiga at quantum-espresso.org> wrote:

> Hello Pier Luigi ,
>
> I forward your email to the q-e-developers mailing-list. I am not expert
> of the physics, I am more on the "computing/HPC" side of things. Hopefully
> someone can clarify this point of you. If it is a bug (it looks like a bug
> and it smells like a bug.... so probably we need to investigate properly)
> we will work to fix it by the official release My uninformed guess is that
> the quantities that varies across different machines is calculated heavily
> using some libraries or some OpenMP. This is something easy to check. I
> cannot comment about cp.x versus pw.x correctness.
>
> Anyone has a guess about these discrepancies or a practical suggestion how
> to verify this?
>
>
> On Sep 13, 2016, at 7:21 AM, Pier Luigi Silvestrelli <
> pierluigi.silvestrelli at pd.infn.it> wrote:
>
> I have found that in QE (in the new 6.0-beta version
> and in previous versions as well) the pressure calculation seems
> to be incorrect using 'cp.x' in combination with non-local vdW-corrected
> functionals, such as vdW-DF, vdW-DF2, vdW-DF-cx, rVV10,...,
> as verified by comparing results obtained using both 'pw.x' and
> 'cp.x' programs.
> For instance, considering a single liquid-water configuration
> and the vdW-DF functional, 'pw.x' (both using the 'scf' and 'md'
> options) gives P=-3.55 kbar, while 'cp.x' gives instead P=200.99 kbar.
> Moreover, P computed by 'cp.x' using the same version of the code
> on different machines gives different results, while all the other
> quantities (total energy,...) are identical.
>
> I would like to let you know this problem, which is of some importance
> for efficient vdW-corrected ab initio MD simulations of liquids.
>
> Thanks in advance. Ciao.
>
> Pier Luigi Silvestrelli
>
> Dipartimento di Fisica e Astronomia G. Galilei
> Via Marzolo 8
> I-35131 Padova, Italy
> tel. +39-049-8277171
> fax  +39-049-8277102
> e-mail : psil at pd.infn.it
>
> --
> Filippo SPIGA ~ Quantum ESPRESSO Foundation ~ http://www.quantum-espresso.
> org
>
>
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>



-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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