Ab initio modeling of spin and charge ordering and lattice dynamicsin 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 Γ 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.