xvii PART I PROPERTIES OF CRYSTALLINE MATERIALS The Effective U in Oxides and in Sulfides: Conceptual Phase Diagrams and their Applications . . . . . . . . . . . . . . .; . . . . . . . . . . . . . . . 1 John B. Goodenough 1. Definitions 1 2. Interatomic interactions 23 References 44 Electron Correlations in Elementary Structures. The Case of Weak Correlations: Metallic and Covalent Bondings . . . . . . . . . . . . . . . . . 45 J. Friedel Introduct i on 45 1. The H2 molecule 46 2. Other elementary diatomic molecules 52 3. Metallic aggregates 53 4. Macroscopic phases of transition metals 57 5....