Model study of the linear density response function - A comparison between the exact result and RPA
The time-ordered linear density response function is examined in a model study. Two model dimers are considered; one with one orbital per site and a second one with two orbitals per site. The one-orbital case has U0, the on-site Coulomb interaction, as the only parameter and is solved analytically. The two-orbital case has parameters U0, the upper orbital non-interacting eigenenergy ε1, and the ho
