Ab initio modeling of spin and charge ordering and lattice dynamics in CaFeO(3) crystals.

Results of first-principles simulations on both orthorhombic and monoclinic phases of CaFeO(3) crystal are presented. The obtained atomic structures are consistent with x-ray diffraction data. The transition from a metallic orthorhombic to a narrow-gap semiconducting monoclinic phase is ascribed to the larger distortion of the Fe-O-Fe bond angle in the latter case. Calculations of Raman and optic active phonon modes at the Gamma point of the Brillouin zone are performed and discussed. The isotopic substitution technique is applied to analyze the vibration modes obtained. The found charge/spin disproportionation is analyzed and compared with available experimental estimates.