  Recent advances in many-body physics have made it possible to study
correlated electron systems at the two-particle level. In Dynamical Mean-Field
theory, it has been shown that the metal-insulator phase diagram is closely
related to the eigenstructure of the susceptibility. So far, this situation has
been studied using accurate but numerically expensive solvers. Here, the
Iterated Perturbation Theory (IPT) approximation is used instead. Its
simplicity makes it possible to obtain analytical results for the two-particle
vertex and the DMFT Jacobian. The limited computational cost also enables a
detailed comparison of analytical expressions for the response functions to
results obtained using finite differences. At the same time, the approximate
nature of IPT precludes an interpretation of the metal-insulator transition in
terms of a Landau free energy functional.
