[Pw_forum] electron-phonon calculation problem

[W2AGZ]

Dear J. Pesic,

I understand your frustration, and Paolo's response is very cogent...the
Fortran "ones and zeroes" at k(q) near zero need to be tuned "a priori or a
posteriori"  in either lambda.f90 and/or its output.  I've dealt with this
issue over the years attempting to calculate the Eliashberg-McMillan strong
coupling superconductivity parameters in copper oxide perovskites.  Please
visit www.w2agz.com for relevant publications/presentations and references.
I've found some success combining algorithms and code from PWSCF, GIBBS2,
and ELK.

I visited and spoke at your institute in Belgade back in "the bad old days"
of the mid-1970s, and recall fondly the hospitality of the faculty and the
beauty of the contryside.

Best, -Paul

-----Original Message-----
From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On
Behalf Of yelena
Sent: Thursday, April 14, 2016 6:49 AM
To: pw_forum at pwscf.org
Subject: [Pw_forum] electron-phonon calculation problem

Dear all,
I've been having problem with electron-phonon calculation. I keep having
negative phonon frequency in gamma point, -0.00007, nowhere else, (so it is
not "real" instability, but some numerical problem) but it keeps interfering
with my lambda.x calculation and all i get is NAN for alpha2F and so on. So
is there any trick to avoid it? This is clearly numerical issue, because
other modes are positive and phonon dispersion looks as it should be and
there is no any instability. Can I somewhere manually change that -, maybe?
I've tried to increase tr2_ph (and decrease it, also) but it keeps happening
just the same. And tried larger k and q grid. Still the same.

Best Regards,
PhD Student J.Pesic
Center for Solid State Physics,
Institute of Physics Belgrade, Serbia


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