[Pw_forum] propagation direction in the input file for dynmat.x
Eyvaz Isaev
eyvaz_isaev at yahoo.com
Thu Apr 16 16:21:33 CEST 2009
Dear Li,
This one can be done using matdyn.x, too.
>My system has hexagonal symmetry and its primitive cell is rhombohedral.
If the difference in between number of atoms not too much, I would prefer hexagonal, as it has higher symmetry and this will make things easier.
>From matdyn.f90:
! Then, if (.not.dos) :
! nq number of q-points
! (q(i,n), i=1,3) nq q-points in 2pi/a units
! If q = 0, the direction qhat (q=>0) for the non-analytic part
! is extracted from the sequence of q-points as follows:
! qhat = q(n) - q(n-1) or qhat = q(n) - q(n+1)
! depending on which one is available and nonzero.
! For low-symmetry crystals, specify twice q = 0 in the list
! if you want to have q = 0 results for two different directions
!
Anyway, you should specify 2 directions like
x(1) y(1) z(1)
........
x(N-1) y(N) z(N)
0 0 0 !!!!! Gamma point x(N)=0 y(N)=0 z(N)=0
x(N+1) y(N+1) z(N+1)
.........
x(M) y(M) z(M)
For a hexagonal lattice you could try A (00z) --> G(000) --> K(-1/3,2/3,0), as example.
Hope this helps.
Bests, Eyvaz.
-------------------------------------------------------------------
Prof. Eyvaz Isaev,
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia,
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden
Condensed Matter Theory Group, Uppsala University, Sweden
Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
--- On Thu, 4/16/09, Li YL <ylli at theory.issp.ac.cn> wrote:
> From: Li YL <ylli at theory.issp.ac.cn>
> Subject: [Pw_forum] propagation direction in the input file for dynmat.x
> To: "pw_forum" <pw_forum at pwscf.org>
> Date: Thursday, April 16, 2009, 4:05 PM
> Dear all users,
>
> Now I've a question on the polar materials. In order to
> get LO-TO splitting, you know, we need to use dynmat.x. In
> the input file for dynmat.x, we need input q(1), q(2), and
> q(3), that is, the propagation direction. I don't know
> how to choose this direction. My system has hexagonal
> symmetry and its primitive cell is rhombohedral.
> Any suggestions are welcome. Thanks in advance.
>
> Bests,
>
> Yanling Li,
>
> Institute of Solid states physics, CAS, P. R. China.
>
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