[QE-users] negative phonon frequency when calculate lambda

[Chao Lei]

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> 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> 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
>> _______________________________________________
>> users mailing list
>> users at lists.quantum-espresso.org
>> https://lists.quantum-espresso.org/mailman/listinfo/users
>
>
>
> --
> Lorenzo Paulatto - Paris
> _______________________________________________
> users mailing list
> users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20181023/c187fdfa/attachment.html>