# [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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```