Study of Ce intermetallic compounds: an LDA classification and hybridization effects

In the last decades, Ce intermetallic compounds have received a lot of attention both in theory and experiment. On one side, these systems can exhibit a large variety of behaviors, such as superconductivity, huge magnetoresistance, itinerant magnetism, etc. On the other side, the nature of the 4f states is controversial since it has not been established yet which systems can be treated using a bandlike picture and which ones using a localized one. In the first picture, the effective electronic correlation is weak and the 4f states form a narrow band, while in the second one, the 4f electrons are highly correlated and interact weakly with the conduction band. The main difference between Ce and other rare earth systems is that, in the case of Ce, the 4f state is energetically very close to the Fermi level so that its occupation number and the strength of hybridization with the conduction electron bands strongly depend on the chemical and geometrical environment. In that sense , we can understand the complexity of the phase diagram of pure metallic Ce which, depending on temperature and pressure, can be magnetic, paramagnetic or superconducting. Due to this fact, different types of magnetism have been observed within the intermetallic compounds: intermediate valence behavior, Kondo effect and magnetic ordered structures (FM, AF) are among them. Intermediate valence behavior appears in systems having the states with n and n− 1 4f electrons almost degenerate. The nearly degenerate condition is a consequence of hybridization of the 4f states and results in a configuration with a non integer electronic occupation number n4f . In general, intermediate valence materials show anomalous values for some physical properties such as lattice parameter, bulk modulus, magnetic susceptibility, etc, as compared to systems