Zhang and Rice derive a single-band effective Hamiltonian for high-temperature superconducting Cu oxides, starting from a two-band model. They show that Cu-O hybridization strongly binds a hole on each O square to the central Cu²⁺ ion, forming a local singlet. This singlet moves through the lattice similarly to a hole in the single-band effective Hamiltonian of the Hubbard model. The key point is that two holes repel each other when on the same square, recovering the single-band model. The Hamiltonian includes terms for Cu and O holes, with hybridization between them. The effective hopping matrix elements are calculated, showing that nearest-neighbor hopping is dominant. The derived effective Hamiltonian is shown to be equivalent to the single-band Hubbard model in the large-U limit. The results support the use of a single-band effective Hamiltonian for Cu-O based compounds, consistent with Anderson's original treatment. The work highlights the importance of phase coherence in producing the large energy separation between different symmetry states. The effective hopping Hamiltonian is reduced to a form that describes the AF interaction between d holes, with the singlet state having no magnetic interaction with other d holes. The effective Hamiltonian is given by $ H_{\mathrm{eff}} = H_{t} + H_{s} $, where $ H_{t} $ and $ H_{s} $ describe the hopping and spin terms, respectively. The results are consistent with experimental data on undoped La₂CuO₄ and support the single-band effective Hamiltonian approach.Zhang and Rice derive a single-band effective Hamiltonian for high-temperature superconducting Cu oxides, starting from a two-band model. They show that Cu-O hybridization strongly binds a hole on each O square to the central Cu²⁺ ion, forming a local singlet. This singlet moves through the lattice similarly to a hole in the single-band effective Hamiltonian of the Hubbard model. The key point is that two holes repel each other when on the same square, recovering the single-band model. The Hamiltonian includes terms for Cu and O holes, with hybridization between them. The effective hopping matrix elements are calculated, showing that nearest-neighbor hopping is dominant. The derived effective Hamiltonian is shown to be equivalent to the single-band Hubbard model in the large-U limit. The results support the use of a single-band effective Hamiltonian for Cu-O based compounds, consistent with Anderson's original treatment. The work highlights the importance of phase coherence in producing the large energy separation between different symmetry states. The effective hopping Hamiltonian is reduced to a form that describes the AF interaction between d holes, with the singlet state having no magnetic interaction with other d holes. The effective Hamiltonian is given by $ H_{\mathrm{eff}} = H_{t} + H_{s} $, where $ H_{t} $ and $ H_{s} $ describe the hopping and spin terms, respectively. The results are consistent with experimental data on undoped La₂CuO₄ and support the single-band effective Hamiltonian approach.