[Pw_forum] sometimes a failure in qvan2.f90

PGnujeon baknoo at tokyo.rist.or.jp
Mon Dec 15 10:24:25 CET 2003

Dear any expert at PWscf ?
When I run pw.x with USPP, sometimes the program stops at qvan2.f90, reporting "invalid mpi operation in qvan2". 
Whenever I encounter such error message, I reduce the number of process and the code works.
Sorry for this rough message. But would any body suggest any hint for this problem ?
Again, "pw.x with USPP" successfully works with some number of processors.
However it fails with some larger number of processors.




----- Original Message ----- 
From: "Paolo Giannozzi" <giannozz at nest.sns.it>
To: <pw_forum at pwscf.org>
Sent: Tuesday, December 09, 2003 10:56 PM
Subject: Re: [Pw_forum] help entreaty

> On Tuesday 09 December 2003 11:43, sprokuda wrote:
> > [...] I get from time to time negative frequencies from PWscf.
> > I have no idea what to do futher in this concern.
> from the last version of the manual:
> * ph.x does not yield acoustic modes with omega(q=0) = 0
>       This may not be an error: the Acoustic Sum Rule (ASR) is never
>       exactly verified, because the system is never exactly translationally 
>       invariant as it should be (see the discussion above).
>       The calculated frequency of the acoustic mode is typically less 
>       than 10 cm^{-1}, but in some cases it may be much higher,
>       up to 100 cm^{-1}. The ultimate test is to diagonalize the
>       dynamical matrix with program "dynmat.x", imposing the ASR.
>       If you obtain an acoustic mode with a much smaller frequency
>       (let us say  < 1 cm^{-1}) with all other modes virtually unchanged,
>       you can trust your results.
> * ph.x yields really lousy phonons, with bad or negative frequencies or
>  wrong symmetries or gross ASR violations.
>       Possible reasons:
>       - Wrong data file file read.
>       - Wrong atomic masses given in input will yield wrong frequencies
>         (but the content of file "fildyn" should be valid, since the force
>          constants, not the dynamical matrix, are written to file).
>       - Convergence threshold for either SCF ("conv_thr") or phonon
>         calculation "tr2_ph") too large (try to reduce them),
>       - Maybe your system does have negative or strange phonon
>         frequencies, with the approximations you used. A negative frequency
>         signals a mechanical instability of the chosen structure. Check that
>         the structure is reasonable, and check the following parameters:
>         - The cutoff for wavefunctions, "ecutwfc"
>         - For US PP: the cutoff for the charge density, "ecutrho"
>         - The k-point grid, especially for metallic systems!
> Paolo
> -- 
> Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
> Scuola Normale Superiore    Phone:   +39/050509412
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