[Pw_forum] quick question about the input file for phonon calculations at a point

[Stefano de Gironcoli]

qx, qy, qz are in unit of 2pi/alat
which means that, for instance,  in a simple cubic lattice the zone 
boundary along x has coordinates (0.5,0.0,0.0) because b1=(1,0,0)*2pi/a
in an fcc lattice the zone boundary in the x direction is instead 
(1,0,0) because in fcc the smallest G vector in that direction is 
(2,0,0)*2pi/a

stefano

On 05/09/2012 09:38 PM, Elie M wrote:
> Dear all, I have a simple question about the coordinates of the point at which one would like to perform phonon calculations. It is just a quick check really. I am talking about the following input file for example:
> Phonon
> dispersion for monolayer grapheme at the gamma point
>
>   &inputph
>
>    tr2_ph=1.0d-14,
>
>    prefix='phmonog',
>
>    trans=.true.,
>
>
>    recover=.true.,
>
>    amass(1)=12.0107,
>
>    outdir='/tmp/',
>
>    fildyn='mgraph.dynG',
>
>    /
>
> qx qy qz<------The point at which the phonon calculation is run.
> In what coordinate system must (qx,qy,qz) be expressed? Is it written in units of 2Pi/alat? and if so, should alat be in Angstroms or a.u.?
> Thanks
> Elie Moujhes
> University of NottinghamNG7 2RDUK 		 	   		
>
>
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