Effect of oxygen content on the energy level of YBa₂Cu₃O_7-δ superconductors

Electronic structures were calculated for a series of YBa₂Cu₃O_7-δ (0 ≤ δ ≤ 1) in different oxygen concentrations by the density function theory (DFT) at BLYP/LanL2MB level by using Gaussian-03 packages. Attentions have been paid especially to the energy level feature near the Fermi level. The results show that the oxygen concentration would greatly influence the energy levels around the highest occupied orbit. When the oxygen concentration increases, the energy level of the highest occupied orbit decreases and the state density increases. This is consistent with the experimental observation of T_c values at different oxygen concentrations.