Different doping from apical and planar oxygen vacancies in   Ba$_{2}$CuO$_{4-\delta}$ and La$_{2}$CuO$_{4-\delta}$
  First principles band-structure calculations for large supercells of Ba$_{2}$CuO$_{4-\delta}$ and La$_{2}$CuO$_{4-\delta}$ with different distributions and concentrations of oxygen vacancies show that the effective doping on copper sites strongly depends on where the vacancy is located. A vacancy within the Cu layer produces a weak doping effect while a vacancy located at an apical oxygen site acts as a stronger electron dopant on the copper layers and gradually brings the electronic structure close to that of La$_{2-x}$Sr$_x$CuO$_{4}$. These effects are robust and only depend marginally on lattice distortions. Our results show that deoxygenation can reduce the effect of traditional La/Sr or La/Nd substitutions. Our study clearly identifies location of the dopant in the crystal structure as an important factor in doping of the cuprate planes. 
T. Jarlborg, B. Barbiellini, R.S. Markiewicz, A. Bansil
cond-mat.supr-con cond-mat.mtrl-sci