Ab initio systematic determination of the t–J effective Hamiltonian parameters for superconducting Cu-oxides

A method for variationally computing the electron transfer integral t and the magnetic coupling constant J within a unified theoretical framework is reported. The method is used to estimate these quantities for the high-Tc La2CuO4 superconductor allowing for an ab initio determination of the Zhang and Rice t–J single-band effective Hamiltonian. It is shown that by using a suitable configuration interaction (CI) space, the magnetic coupling can be rationally and quantitatively determined. On the other hand, the analysis of the final CI eigenvectors shows that hole doping involves states in which the hole has a large oxygen contribution in agreement with experiment.