Renormalization from density-functional theory to strong-coupling models for electronic states in Cu-O materials

Strong-coupling models for the electronic structure of La₂{CuO}₄$ are derived from the local-density-functional results in two successive stages of renormalization. First, a three-band Hubbard model is derived with parameters explicitly calculated from first principles using a constrained density-functional approach and a mean-field fit to the Cu-O pd{σ} bands. Second, exact diagonalization studies of finite clusters within the three-band Hubbard model are used to select and map the low-energy spectra onto effective one-band Hamiltonians, e.g., the Heisenberg, one-band Hubbard, or ``t-t'-J'' model. At each stage, calculated observables are in quantitative agreement with experiment.