[Pw_forum] start_q, last_q, start_irr, last_irr

Elie Moujaes elie.moujaes at hotmail.co.uk
Wed Jun 2 15:30:53 CEST 2010

Dear Eyvaz and Jeff,


Thank you very much for your help. The reason I am doing this is that I am still trying to get the phonon dispersion but using other this new technique implemented in version 4.2 of QE. Everything is going well except that for q-0 (the Gamma point), I am getting an error


     from davcio : error #        20
     error while reading from file


The strange thing is that only for this point, I obtain such an error...I guess another guy posted that error earlier with the title Phonon calculations on the Grid. His name is shining star.   


Jeff, thanks for your suggestion as well. Actually i am still looking at the phono dispersion as a whole but found this technqieu which merges all files at the end and takes less time (I hope!).





Elie Moujaes

University of Nottingham


> Date: Tue, 1 Jun 2010 15:39:07 -0700
> From: eyvaz_isaev at yahoo.com
> To: pw_forum at pwscf.org
> Subject: Re: [Pw_forum] start_q, last_q, start_irr, last_irr
> Dear Elie,
> --- On Wed, 6/2/10, Elie Moujaes <elie.moujaes at hotmail.co.uk> wrote:
> >I am trying to get the phonon dispersion of graphene by taking each q on >its own and performing the necessary operations (i.e using start_q, >last_q, start_irr, last_irr) then merging the points all together . Can >anyone please explain to me more about these parameters.
> I never used  start_irr, last_irr, but I use actively start_q and last_q parameters. After you get all dynX (including dyn0) files, just collect them in a directory and run q2r.x.
> start_q - q-point from which ph.x starts, last_q - up to this q-point from the list of q-points written in dyn0-file. I.e. if you have 12 q-points according to dyn0-file, then you can choose any combination, start_q=1, last_q=1 (usually this one is the Gamma point), or start_q=9, last_q=12 (calculate phonons for q-points from 9th to 12th), or any other combination you like (sure, last_q >= start_q).
> The same meaning for start_irr and last_irr, but for irreducible representations.
> >I read the INPUT_PH and the examples in GRID but did not actually >understand what these mean..I got that irr is irreducible representation >but how can one set these each time one runs the calculation for a q.
> Specify in ph.in files the next lines:
> *****
> start_q=M
> last_q=N
> start_irr=I1
> last_irr=I2
> If M=N, only irreducible representations (IrRep) in the range I1 - I2 will be calculated for a given (defined by M) q-point. By default, all IrRep will be calculated. 
> So easy!
> Bests,
> Eyvaz.
> -------------------------------------------------------------------
> Prof. Eyvaz Isaev, 
> Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
> Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
> isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
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