[Pw_forum] Question on el-ph calculations

Paolo Giannozzi paolo.giannozzi at uniud.it
Thu Apr 23 19:45:45 CEST 2015

The convergence of electron-phonon coefficient calculations is invariably slow and difficult. Even more so in systems like boron-doped diamond, presumably having a small Fermi surface. There are no simple solutions, to the best of my knowledge.


From: pw_forum-bounces at pwscf.org <pw_forum-bounces at pwscf.org> on behalf of MKondrin <mkondrin at hppi.troitsk.ru>
Sent: Thursday, April 23, 2015 18:00
To: Сергей Ерохин; PWSCF Forum
Subject: Re: [Pw_forum] Question on el-ph calculations

Сергей Ерохин wrote:
> Dear Dr. Kondrin,
> Thank you for your answer, however I found in the forum that
> ||||||||||||||||||||||||||||
> If your k point grid is fine enough, if you plot lambda as a function of
> the broadening there is a plateau, i.e. it looks like this:
> lambda
> ^
> |/\
> /|/ \
> /|/   \______    <-- converged value
> /|/                  \
> /|/_________\__> broadening
> /
> The correct value of lambda is the one on the plateau
> http://qe-forge.org/pipermail/pw_forum/2014-October/105303.html
> |||||||||||||||||||||||||||||
> And I wonder what value of broadening should be taken to get this
> plateau. Understand that this value must be small but how far. Could I
> expect that in my case the plateau at broadening ~0.2.
> --
> Sergey Erohin
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Dear Sergey!

First, in your case it is not quite clear what is plateau. Second, in
the thread you cited degauss values are well below 0.1. If you are
interested in superconducting properties you should consider quite low
temperatures (around Tc), so there is no reason why electron
distribution function should be very broaded. Larger degauss values mean
larger temperature which in its turn destroy superconductive state. So
your graph (if one does not take into account too large degauss values)
just illustrate this.

Best regards,
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