REALISTIC ELECTRONIC-STRUCTURE CALCULATIONS FOR MAGNETIC INSULATORS LIKE LA2CUO4

We suggest that Hartree-Fock theory is a good starting point for the solution of ab initio-derived extended Hubbard Hamiltonians for magnetic insulators like La2CuO4, as indicated by surprisingly accurate results for the superexchange frequencies and insulating gaps for this material and isostructural La2NiO4, K2CuF4, and K2NiF4. Limited configuration interaction beyond Hartree-Fock theory is then used to demonstrate that admixtures of a1 (d3z2-r2) symmetry states at energies somewhat away from the gap edge are essential to the dispersion of the first quasiparticle branch in La2CuO4 for doped-in holes.