SURFACE MAGNETISM IN AN EXACTLY SOLUBLE MANY-BODY PERIODIC-CLUSTER MODEL OF BCC IRON

An exact solution of a two-dimensionally periodic two-site cluster, a {001} two-layer thin film with body-centered-cubic (bcc) crystal structure, is presented for iron. The purpose is to study the surface magnetism of bcc iron in a full many-body approach. The model consists of five d orbitals per site per spin, with interatomic hopping terms, a one-electron occupation energy for each orbital, and an on-site Coulomb interaction of the fullest generality allowed by atomic symmetry. A realistic local-density-approximation single-particle electronic structure is used. Crystal-field effects in the iron-film structure are discussed. The many-body energy-level spectrum and thermodynamic averages of energy and spin of the system are calculated. The physical picture for the enhancement of magnetization at the true iron surface is discussed. © 1990 The American Physical Society.