[Pw_forum] M3 phonon degeneracy of ReO3

[Paolo Giannozzi]

On Saturday 14 May 2005 02:55, W. YU wrote:

> I am now doing first principles phonon dispersion
> caculations using PW on a system similar to ReO3(
> which is ABO3 perovskite structure without A atom).
> [...] the soft phonon M3 mode is said to be triply
> degenerate corresponding to the Octhedra rotation
> around three principle axes. But from theoretical
> analysis, as done by E. Wigner (Phys. Rev. V50,
> 58(1936)) and R. A. Cowley (Phys. Rev. V134 A981
> (1964)), there is no triply degenerate modes at M
> point, only doubly degenerate and nondegenerate
> modes. Especially, the M3 mode is nondegenerate.

I know nothing about the specific materials, so I am
just guessing: maybe at each q-vector M the M3 modes
is nondegenerate, but there are three distinct q-vectors
for M, related by symmetry?

Paolo

-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
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