ORBITAL AND CHARGE ORDERING IN PR1-XCAXMNO3 (X=0 AND 0.5) FROM THE AB-INITIO CALCULATIONS

The electronic structure of the doped manganites Pr1-xCaxMnO3 was calc ulated by the LSDA + U method which takes into account the local Coulo mb interaction between d electrons of transition-metal ions. In contra st to the standard local-spin-density approximation, no Jahn-Teller la ttice distortions are needed to reproduce the experimentally observed orbital ordering in the undoped PrMnO3. The correct ground state, a ch arge and orbital ordered antiferromagnetic insulator, was obtained for Pr1/2Ca1/2MnO3. The results are in a good agreement with the neutron- diffraction data.