Ab initio study of the optical phonons in 1D antiferromagnet Ca2CuO3
  In the spin 1/2 antiferromagnetic Ca2CuO3 the optical excitation along 1D a Cu-O chain showed the enrichment of forbidden peaks that could not be explained by the group theory. We present the cluster-model ab initio study of these optical phonons based on the Hartree-Fock SCF calculation with the 3-21G basic set. The obtained results showed very good agreement with the observed data. The Cu-O resonances generally showed the lower shifts in Ca2CuO3 than in pure CuO and were primarily composed of the vibrations of the oxygen in static host lattice whereas the Cu movements happened only in the collective lattice vibrations. Almost complete classification of the forbidden phonons is presented. 
Nam Nhat Hoang, Thu Hang Nguyen, and Chau Nguyen