[Pw_forum] epsilon.x

[Andrea Ferretti]

Dear Pashangpour,

the idea is very similar to the usual kpt convergence 
vs smearing parameter for a DOS calculation.

At variance with scf runs, here you are computing a spectral quantity 
(the dielectric function as a function of the frequency), meaning that you 
may need a (much) finer mesh of kpts.

In general, the larger the smearing, the lower the resolution of your 
spectrum (in the simplest case you are replacing dirac's deltas with 
gaussians), while the larger the kpt mesh that you use, the smaller the 
smearing parameter can be...

I would follow a recipe like this:
* set the smearing and converge the spectrum wrt kpts
* if the accuracy of the spectrum (ie the resolution of its features) is
   ok with you, exit(),
   otherwise reduce the smearing parameter and iterate
* by reducing the smearing you should expect to converge with a denser
   mesh of kpts  (a rule of thumb could be dk * delta ~ constant, where
   dk is the kpt grid spacing and delta the smearing parameter.. though
   it probably depends on the system and on your requirements)

Andrea


> Dear all
> How can I find suitable value of intersmear and intrasmear in epsioln calculation via epsilon.x?
> Thanks in advance
> M. Pashangpour
> PhD of physics
> IAU,Tehran,Iran
>
> Sent from my iPhone
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-- 
Andrea Ferretti, PhD
S3 Center, Istituto Nanoscienze, CNR
via Campi 213/A, 41125, Modena, Italy
Tel: +39 059 2055322;  Skype: andrea_ferretti
URL: http://www.nano.cnr.it