[Pw_forum] ele phonon coupling at the gamma point

Elie M elie.moujaes at hotmail.co.uk
Tue Oct 2 18:42:58 CEST 2012

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    0.847800I 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 MUniversity of NottsNG7 2RDUK 		 	   		  
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