Theories for Many-Electron Systems with Strong Electron—Phonon and Interelectron Coulombic Interactions

The main objective of solid state theory is to clarify the microscopic origins of various macroscopic properties of solids, such as electric, magnetic and optical properties, which change from one crystal to the other. The difference of these macroscopic properties between crystals mainly originates from the difference of the microscopic nature of electrons in each crystal. In particular, it mainly comes from the outer electrons, which are in the outermost orbitals of the atoms or molecules constituting each crystal. Consequently, one of the most important problems in solid state theory is to find the relation between the microscopic nature of the outermost electrons and the macroscopic properties of solids.