[Pw_forum] propagation direction in the input file

[Eyvaz Isaev]

Dear Li,

--- On Fri, 4/17/09, Li YL <ylli at theory.issp.ac.cn> wrote:
 
>  Many thanks your suggestions or comments.  

Welcome!

> Can you give me example file to finish  LO-TO spliting
> using matdyn.x? 

See attached file.  But keep in mind IFC (and the dynamical matrix at Gamma point)  have to be calculated as an insulator (semiconductor). I.e. there is no need to specify occupations (and related keywords) in scf.in. 
At the same time add epsil=.true. to ph.in. This will give you IFC and dyn0 files with macroscopic dielectric constants and Born effective charges.

Attached file is for a hexagonal lattice. You can not use it directly as you have to use your actual c/a ratio.

> I noticed that for insulator,  by default,
> ph.x firstly calculate electric field and effective charges.
> Why?   
>  
ph.x does not calculate electric field, it calculates macroscopic dielectric constants and Born effectife charges.
Because of that LO-TO splitting depends on these parameters.  

Please read a textbook why this LO-TO splitting occurs.

> There are 30 atoms in unit cell. But in its primitive cell,
> the number of atoms is only 10. 
> 
Well, I see. Sure the primitive cell is more suitable.

> By the way, now I can obtain dielectriic constants (high
> frequency dielectric constants) and effective charges, but I
> don't know how to get static dielectrin constant and
> polar charges? can you give me some suggestions? 

Again, not "polar" charges, Born effective charges.

Static dielectric constants and the charges can be calculated easily. See above. 

Bests,
Eyvaz.

> 
> Best regards, 
> 
> Yanling Li, 
> 
> Institute of solid states physics, CAS, China.
> 
> 
> -------------------------------------------------------------------------
> 
> >>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.
> 
> 
> >--- On Thu, 4/16/09, Li YL
> <ylli at theory.issp.ac.cn> wrote:
> 
> > 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.
> 
> 
> Re: [Pw_forum] propagation direction in the input file
> 
> 
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