Fermi-surface pockets in YBa2 Cu3 O6.5: Comparison of ab initio techniques

We study the Fermi surface of metallic, nonmagnetic ortho-II YBa2 Cu3 O6.5 using three different density-functional-based band-structure techniques [generalized gradient approximation (GGA), GGA+U, and pseudo-self-interaction correction (PSIC)]. The calculated Fermi surface exhibits no pockets in GGA+U and PSIC, and a minor one in GGA. Upon shifting the Fermi level in the vicinity of the calculated value, we instead observe several pocket structures. We calculate their cross-sectional areas and cyclotron masses. Overall, our calculations show no solid evidence of the existence of electronlike-nor, in fact, of any-Fermi-surface pockets in this phase. This suggests that the origin of the pockets should be sought for in other different phases.