[Wien] Phonon calculation

[Madesis Ioannis(John)]

> John
> 
> 1) If you need to use P1 symmetry try a extremely small displacement
>   of your atoms to force the reduction of symmetry you need.
> 2) Notice that symmetry is used by the codes to reduce the 
> computational
>   effort. The other route is better if you hace time, experience and
>   the capacity to improve Phonopy: use symmetry in the analysis.
> 
> Regards,
>       Dr. Víctor Luaña


Thank you for your answer Dr.Luaña
I fear that the answer might not be that simple, but please correct me 
if I am wrong.

1)Regarding the displacements, they are generated automatically by 
Phonopy. The only accessible variable is the size of the displacement. 
The choice of which atom, and towards what direction is something I 
cannot control.

2)I couldn't agree more, regarding the symmetry. However, one must have 
an idea of how Phonopy works. Phonopy displaces an atom, and with the 
help of the electronic structure calculation, it measures the effect on 
the forces of all the other atoms. Having a type of symmetry, would lead 
to more than one displacements inside the unit cell, since the 
displacement would occur on all EQUIVALENT atoms, thus compromising the 
effect the displacement has on the other atoms.

And a new question for now: Since the idea seems to work nice, are there 
any other converged data that could be transferred to the calculations 
to be? If one could compare *.klist files, and find them identical, 
could any plane-wave information be transferred?

-- 
Ioannis Madesis (Μαδέσης Ιωάννης)
PhD Student
Atomic and Molecular Physics
Department of Physics
University of Crete
(0030)-210-6503598