[Pw_forum] M3 phonon degeneracy of ReO3

W. YU yuwen_66 at yahoo.com
Sat May 14 04:55:50 CEST 2005

Dear PW users, 

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).
For this reason, I have read several papers concerning
this structure including PRB V33, 4793 (1986). In this
paper( also in the paper by J. D. Axe cited by this
paper ), 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. My
calculation also similar to the theoretical analysis.
But since several well cited papers mentioned the
triplet degeneracy of M3, I am confused about this.
Maybe I misunderstood something here, but I just
couldn't figure it out.

This question may be unsuitable for this group, but I
can't find the original authors such as J. D. Axe
's information to consult. So I post it here, hope
someone might be interested in it. Your kind reply
would be much appreciated.



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