Photoemission, inverse photoemission, and fluctuations in an exactly soluble many-body cluster model of bcc iron

An exact solution for a two-site crystal model, the smallest body-centered-cubic crystal, is presented for iron. The model consists of five d-like orbitals per site per spin, with interatomic hopping terms and an on-site Coulomb interaction of the fullest generality allowed by atomic symmetry. The ground state, depending on the choice of one-electron parameters, is found in one case to be a fully saturated ferromagnet, and in another to be an unsaturated ferromagnet with strong antiferromagnetic fluctuations. The many-body energy-level spectrum, intracluster charge and spin fluctuations, and photoemission and inverse photoemission densities of states for both cases are calculated and compared with experiment.