ABSTRACT
There has been an immense interest in the strongly correlated systems over the past several decades arising from a wide spectrum of exciting properties exhibited by them. These properties are evidently related to the existence of strong electronelectron interactions within some partially occupied orbitals, as the not-so-strongly correlated analogues of such systems do not exhibit these interesting properties. For example, several intermetallic compounds of Ce with its nearly 4/ 1 config uration exhibit the phenomenon of heavy fermion superconductivity, while the corresponding La compounds with 4 f ° configuration do not. Similarly, it is well known that strong electron-electron interaction effects within the Cu 3d manifold are crucial for the high temperature superconductivity of the cuprates. It is not possible to describe the electronic structure and related properties of such strongly correlated systems within the ab initio band structure theories, as the strong inter actions preclude the possibility of any effective single-particle description. In such cases, the systems are often described by model Hamiltonians containing a single electron part and a part describing the many-body correlation effects. In order to derive physical properties from these model Hamiltonians that are relevant for a given material, it is crucial to have realistic estimates of the material-specific parameters entering these model Hamiltonians.
