Tetrahedral magnetic cluster embedded in metallic matrix: electron-correlation effects

A tetrahedral magnetic cluster surrounded by metallic atoms is studied in the framework of the Hubbard model. The ground-state energy and the wave function are obtained exactly using the Lanczos numerical diagonalization method. The spin/spin correlation functions /spl gamma//sub ij/= and the total spin S are analyzed as a function of the ratio between the on-site Coulomb repulsion U and electronic hopping t.