[Pw_forum] ele phonon coupling at the gamma point

[Elie M]

> There are several gazillions of papers dealing with electron-phonon
> coefficients in graphene.
I was not clear enough: Sorry my fault. My concern is not graphene. I have already done calculations for graphene long time ago with 20 phonon wave vectors and got reasonable results comparable to those found in the literature (~ 0.02 which are obviously different from the ones below found when only the Gamma point is involved).  My project involves around 40 atoms in the supercell and since phonon calculations over the whole dispersion range is really computationally expensive, I am only doing them at the Gamma point and I want to know how efficient are such calculations, hence why I decided to repeat the calculations for graphene at only the Gamma point for comparison purposes. 
>As far as I know, option electron_phonon='simple'
> should work for a single phonon wave-vector.
Thanks. i will try to repeat the calculations at Gamma using this option.
Elie

> From: giannozz at democritos.it
> Date: Tue, 2 Oct 2012 19:36:47 +0200
> To: pw_forum at pwscf.org
> Subject: Re: [Pw_forum] ele phonon coupling at the gamma point
> 
> 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
> > _______________________________________________
> > Pw_forum mailing list
> > Pw_forum at pwscf.org
> > http://pwscf.org/mailman/listinfo/pw_forum
> 
> ---
> Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
> 
> 
> 
> 
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