Competing crystal structures in La0.5Ca0.5MnO3:: Conventional charge order versus Zener polarons -: art. no. 085125

Equilibrium crystal structures for La0.5Ca0.5MnO3 have been calculated using hybrid Hartree-Fock and density functional methods. Two distinct ground states with either conventional checkerboard charge ordering, in which Mn ions have formal valence 3 or 4, or Zener polaron formation, in which each Mn ion has valence 3.5, are found depending on the proportion of Hartree-Fock exchange used. These structures correspond to those identified by various experiments and they differ by small displacements of key oxygen ions.