  In the present work we report the band structure calculations for the high
temperature superconductor Nd$_{2-x}$Ce$_x$CuO$_4$ in the regime of strong
electronic correlations within an LDA+GTB method, which combines the local
density approximation (LDA) and the generalized tight-binding method (GTB). The
two mechanisms of band structure doping dependence were taken into account.
Namely, the one-electron mechanism provided by the doping dependence of the
crystal structure, and the many-body mechanism provided by the strong
renormalization of the fermionic quasiparticles due to the large on-site
Coulomb repulsion. We have shown that in the antiferromagnetic and in the
strongly correlated paramagnetic phases of the underdoped cuprates the main
contribution to the doping evolution of band structure and Fermi surface comes
from the many-body mechanism.
