  The local electronic structures of La2CuO4, three members of the
Yttrium-family (YBa2Cu3O6, YBa2Cu3O7, and YBa2Cu4O8), and to some extent of
Nd2CuO4 have been determined using all-electron ab-initio cluster calculations
for clusters comprising up to thirteen planar copper atoms associated with
their nearest planar and apical oxygen atoms. Spin-polarized calculations in
the framework of density functional theory have enabled an estimation of the
superexchange couplings J. Electric field gradients at the planar copper sites
are determined and their dependence on the occupation of the various atomic
orbitals are investigated in detail. The changes of the electronic field
gradient and of the occupation of orbitals upon doping are studied and
discussed. Furthermore, magnetic hyperfine fields are evaluated and
disentangled into on-site and transferred contributions, and the chemical
shifts at the copper nucleus are calculated. In general the results are in good
agreement with values deduced from experiments except for the value of the
chemical shift with applied field perpendicular to the CuO2-plane.
