[QE-users] negative phonon frequency when calculate lambda
Lorenzo Paulatto
paulatz at gmail.com
Mon Oct 29 09:52:26 CET 2018
Matdyn just interpolates the 2-body force constants to get the dynamical
matrix at an arbitrary q point and diagonalizes it. It does not care if
the frequencies are positive or negative, it also does not compute any
electron-phonon coupling.
kind regards
On 23/10/2018 23:21, Chao Lei wrote:
> Hello, Lorenzo,
>
> Thanks for your reply, I am using matdyn.x and it already got the lambda
> vs broadening without NaN or mathematical errors, the negative frequency
> makes sense for me. So in matdyn.x the code does not do any check on the
> frequencies too ? or it just neglected the negative frequency when doing
> the sum ?
>
> Best wishes
>
> Chao Lei
> Pos-doc
> The University of Texas at Austin
>
> On Tue, 16 Oct 2018 at 02:43, Lorenzo Paulatto <paulatz at gmail.com
> <mailto:paulatz at gmail.com>> wrote:
>
> Hello Chao,
> do you mean, if you can compute lambda, or you have computed it
> already and you are asking if it makes sense?
> THe big problem with negative frequencies with this kind of system
> is that you cannot really impose conservation of energy, but as in
> elph conservation of energy is maybe not crucial. Anyway, the
> original lambda.x code does not do any check on the frequencies, so
> you probably get NaN or mathematical errors if you try to use it.
>
> Lambda.f90 is a very simple code, I think you may try to edit it and
> see if different recipes can give something reasonable (i.e. skip a
> mode when w2 is negative, use a complex omega=sqrt(w2) but take
> delta( |e-omega|)...), sum the contribution with a weight
> exp(-IMAG(omega)/something),....
>
> Of course, playing with the code can help thinking, but does not
> replace it.
>
> cheers
>
> On Mon, 15 Oct 2018 at 18:22, Chao Lei <leichao.forum at gmail.com
> <mailto:leichao.forum at gmail.com>> wrote:
>
> Dear users,
>
> I am calculating electron-phonon using ph.x, which got negative
> frequency. This is OK for me as it is expected, however, I have
> a question that how does ph.x treat the negative frequency when
> use them to calculate the electron-phonon coupling constant
> lambda ? Thanks for your reply
> if you know the answer.
>
> Best
>
> Chao Lei
> Pos-doc
> The University of Texas at Austin
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> --
> Lorenzo Paulatto - Paris
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