Abstract:
Electronic correlations play the central role in governing many fundamental
aspects of materials, which include excitation characteristics, thermodynamic
and dynamic behavior of systems, ranging from small molecules to solids
and complex systems like DNA and protein. Depending upon the strength
of electronic correlations, the materials world can be categorized into two
broad classes: (i) strongly correlated and (ii) weakly correlated electronic
systems.
In strongly correlated systems, the Coulomb interaction energy is comparable or greater than the kinetic energy. Examples of a few strongly correlated electronic systems include cuprates, rare-earth lanthanides and actinides, vanadates, manganites and transition metal oxides. A number of
novel properties emerge due to electron-electron interaction [1–5]. Over past
few decades, the strongly correlated materials have been of great interest to
both theorists and experimentalists alike, owing to their unusual electronic and magnetic properties [6–22]. Because of the advancement of quantum mechanics, the essential features of these wide class of materials are explained by
many-particle theory since the independent particle picture fails to describe
the strongly correlated systems. However, the weakly correlated materials
in which the electron-electron interaction is weak or negligible, can be well
described by various one electron theories.
