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 Scuola Normale Superiore Phone: +39/050-509876, Fax:-563513 Piazza dei Cavalieri 7 I-56126 Pisa, Italy
