[Pw_forum] ele phonon coupling at the gamma point

[Paolo Giannozzi]

There are several gazillions of papers dealing with electron-phonon
coefficients in graphene. It shouldn't be difficult to find some data
to compare with. As far as I know, option electron_phonon='simple'
should work for a single phonon wave-vector.

P.

On Oct 2, 2012, at 18:42 , Elie M wrote:

> Dear all,
>
> I am trying to do el-ph calculations only at the Gamma point for  
> graphene (as I want to compare it to another system where the  
> calculations are only feasible at the Gamma point). However the  
> values I am getting for lambda for graphene  AT THE GAMMA POINT are :
>
> degauss   lambda
>
>   0.005   13.442600
>
>   0.015    2.303600
>
>   0.020    1.756000
>
>   0.025    1.436000
>
>   0.030    1.228800
>
>   0.035    1.085800
>
>   0.040    0.983000
>
>   0.045    0.906400
>
>   0.050    0.847800
> I am using a 90 x90 x1 grid (in scf) for graphene and the ph file  
> has only one point nq1=0 nq2=0, nq3=0 (the Gamma point).
>
> It is already known that lambda for graphene is  ~0.02.
> (1) Do the above results mean that one cannot calculate el-ph  
> coefficients unless on a grid of phonons and then are the  
> calculations -at the Gamma point ONLY- useless and unexact?
>
> (2) or does this mean that the results did not converge due to a  
> small k-mesh in the scf calculations (90x90x1) and I need to  
> increase it to say 400x400x1?
>
> Any suggestions of any kind would also be ahighly appreciated.
>
> Thanks for your help
>
> Elie M
> University of Notts
> NG7 2RD
> UK
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---
Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222