Temperature dependence of the electronic structure of La₂CuO₄ in the multielectron LDA+GTB approach

The band structure of La₂CuO₄ in antiferromagnetic and paramagnetic phases is calculated at finite temperatures by the multielectron LDA+GTB method. The temperature dependence of the band spectrum and the spectral weight of Hubbard fermions is caused by a change in the occupation numbers of local multielectron spin-split terms in the antiferromagnetic phase. A decrease in the magnetization of the sublattice with temperature gives rise to new bands near the bottom of the conduction band and the top of the valence band. It is shown that the band gap decreases with increasing temperature, but La₂CuO₄ remains an insulator in the paramagnetic phase as well. These results are consistent with measurements of the red shift of the absorption edge in La₂CuO₄ with increasing temperature