Electronic spectra and possible Jahn-Teller distortions in La-(Ba,Sr)-Cu-O superconducting systems

Abstract

We study the possibility for the existence of Jahn-Teller distortions in the La-(Ba,Sr)-Cu-O system. The Jahn-Teller analysis is based on the calculation and correspondingly group theory classification for the electron spectra of the CuO6 elongated octahedra cluster, having the symmetry group D-4h. The motivation to study this model is that the origin of the apical deformation is not a pure Jahn-Teller effect, having therefore a non a priori condition to remove all the degeneracy of the ground state electronic wave function of the regular octahedron with O-h symmetry. This is based on an ab initio calculation of the electronic ground state of the cluster representing the above mentioned system, using an open shell restricted and unrestricted Hartree-Fock (RHF-OS,UHF) wave functions for several basis sets. The system is formed with a total of 87 electrons, with 44 and 43 occupied alpha and beta orbitals respectively for the UHF calculation. We present a comparative analysis of the symmetry classified electron spectra for each of the above mentioned calculations including polarized states. It is shown that in all cases the HOMO states for partially filled levels are not degenerate given therefore a nondegenerate total electronic ground state wave function. Based on this analysis we do not find, within the cluster approximation and the use of HF wave functions, the necessary condition for the fulfillment of the Jahn-Teller theorem.