  Holes doped within the square CuO2 network specific to the cuprate
superconducting materials have oxygen 2p character. We investigate the basic
properties of such oxygen holes by wavefunction-based quantum chemical
calculations on large embedded clusters. We find that a 2p hole induces
ferromagnetic correlations among the nearest-neighbor Cu 3d spins. When moving
through the antiferromagnetic background the hole must bring along this spin
polarization cloud at nearby Cu sites, which gives rise to a substantial
reduction of the effective hopping parameters. Such interactions can explain
the relatively low values inferred for the effective hoppings by fitting the
angle-resolved photoemission data. The effect of the background
antiferromagnetic couplings of renormalizing the effective nearest-neighbor
hopping is also confirmed by density-matrix renormalization-group model
Hamiltonian calculations for chains and ladders of CuO4 plaquettes.
