Density functional electronic spectrum of the $Cu O_{-6}^{-10}$ cluster and possible local Jahn-Teller distorsions in the La-Ba-Cu-O superconductor

TL;DR

This study uses DFT calculations to explore local distortions in CuO6 clusters within La-Ba-Cu-O superconductors, suggesting a possible pseudo Jahn-Teller effect influencing structural distortions.

Contribution

It provides a comparative analysis of DFT and UHF methods, revealing the electronic ground state characteristics relevant to Jahn-Teller effects in the superconductor.

Findings

Both DFT and UHF yield non-degenerate ground states, ruling out pure JT effects.

DFT shows a near-degenerate E_g state, indicating potential PJT influence.

Study suggests local distortions may be driven by PJT effects rather than pure JT distortions.

Abstract

We present a density functional theory (DFT) calculation in the generalized gradient approximation to study the possibility for the existence of Jahn-Teller (JT) or pseudo Jahn-Teller (PJT) type local distortions in the La-Ba-Cu-O superconducting system. We performed the calculation and correspondingly group theory classification of the electronic ground state of the CuO${_{6}}^{-10}$ elongated octahedra cluster, immersed in a background simulating the superconductor. Part of the motivation to do this study is that the origin of the apical deformation of the CuO${_{6}}^{-10}$ cluster is not due to a pure JT effect, having therefore a non {\it a priori} condition to remove the degeneracy of the electronic ground state of the parent regular octahedron. We present a comparative analysis of the symmetry classified electron spectrum with previously reported results using unrestricted Hartree-Fock calculations (UHF). Both the DFT and UHF calculations produced a non degenerate electronic ground state, not having therefore the necessary condition for a pure JT effect. However, the appearance of a degenerate E$_{g}$ state near to the highest occupied molecular orbital in the DFT calculation, suggests the possibility for a PJT effect responsible for a local distortion of the oxidized CuO$_{6}^{-9}$ cluster.