Functional Integral Approach for an Extended Hubbard Model: Two‐Centre Coupling

Abstract

Abstract The behaviour of two neighbouring magnetic centres imbedded in an effective energy band is studied with the aid of the functional integral formalism. The model includes the parts of intra‐atomic and inter‐atomic Coulomb interaction which can be written in terms of occupation number operators. Orbital degeneration is not considered. The magnetic susceptibility calculated within the static approximation gives a continuous interpolation between the Pauli‐band susceptibility and the case of two ferromagnetically or antiferromagnetically coupled Ising spins in the atomic limit.