Another analysis technique common to electronic structure theory is the density difference function, which is capable to illustrate the change of the electron distribution in a molecule upon excitation. More specifically, these can be defined in two ways: (I) the difference between the density of polaritonic state |Ψ a ⟩ inside and an analogous electronic state outside the cavity |ψ α ⟩ ⊗ |n⟩ (usually the ground polariton state and the ground electronic states) and (II) the difference between the density of one polaritonic state |Ψ a ⟩ and another state |Ψ b ⟩ (usually for ground and an excited polariton state). Fig. describes the density difference of type (I) for the ground state while Fig. for the same molecular shows the difference density of type (II) for the polaritonic excited state and ground state. In Fig. , the ground state density difference (∆ρ(z) = ρ cav 00 (z) -ρ nocav 00 (z)) is presented where the cavity (with coupling λ = 0.05 a.u.) is placed in resonance with the lowest-lying charge transfer state (from NH 2 group to the NO 2 group, see panel d for molecule) and showcases a modulation of the ground state indicating charge displacement, where blue and red isosurfaces represent charge accumulations and depletions, respectively. A charge migration of -0.005 |e|, induced by the cavity, is seen from the acceptor (NO 2 ) to the nitrogen atom of the donor (NO 2 ), effectively reducing the ground state dipole from 6.87 D to 6.77 D. This reduction in dipole moment is thought to by a direct result of the cavity inducing charge migration in order to reduce the variation in the dipole ∆μ (see discussion near Eq. 124). Here, ∆ρ