[Pw_forum] start_q, last_q, start_irr, last_irr

[Eyvaz Isaev]

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