MOLECULAR-ORBITAL CLUSTER CALCULATIONS ON YBA2CU3O7, PRBA2CU3O7, NDBA2CU3O7, HOBA2CU3O7 AND CMBA2CU3O7

We present and analyze the results of crystal-embedded molecular-orbital calculations for several members of the orthorhombic MBa2Cu3O7 series: M = Y, Pr, Nd, Ho or Cm. Most of our results are nonrelativistic but we also report some fully relativistic results for the Cm compound. Calculated charge distributions indicate trivalent behavior for all these compounds. For Ho, Nd, Pr, and Cm, the orbital character of the primarily f-electrons changes greatly. Only Ho and, to a lesser extent, Nd show the classically expected isolation of the f-orbitals from mixing with orbitals of other atoms. For the occupied molecular orbital of the Pr and Cm compounds, the energy eigenfunctions show unusual mixing between the f-orbitals and the d-orbitals of the planar-coordinated Cu atoms. These results correlate well with the presence or absence of superconductivity for the various members in the series. © 1990.