In this paper, from the microscopic Hubbard Hamiltonian we extract the local spin-singlet amplitude due to short-range spin correlations and quantify its strength near half-filling. As a first application of the present approach, we study the problem of the energy dispersion and its d-wave modulation in the insulating cuprates ${\mathrm{Sr}}_2{\mathrm{CuO}}_2{\mathrm{Cl}}_2$ and ${\mathrm{Ca}}_2{\mathrm{CuO}}_2{\mathrm{Cl}}_2.$ Without any adjustable parameters, most puzzling issues are naturally and quantitatively explained within the present approach.

• Received 25 September 2000

DOI:https://doi.org/10.1103/PhysRevB.63.214505