Electron structure and phonon spectra anomalies in oxide HTS

The new results on the HTS phonon spectra with anomalous softening of LO ph onon frequency omega (LO) were analyzed. These data could be understood as a consequence of charge superstructure in the oxygen sublattice in addition to metal sublattice ordering. The charges and spin ordering produce the do ubling of lattice periods and new Brillouin zone. Doping leads to the Fermi surface with sides parallel to [100] directions. These results agree with experimental data. The phonon spectra anomalies might be associated with th e nesting conditions between the congruent parts of the Fermi surface.