where ĤM is the molecular Hamiltonian, Ĥph is the photon field Hamiltonian, â † and â are the raising and lowering operators of the cavity field, and μ is the dipole operator of the molecule. Further, χ = χê, where χ describes the coupling strength, and ê indicates the cavity field polarization direction. This Hamiltonian predicts that there will be couplings between the photon-dressed states, for example, |g, 1 ≡ |g ⊗ |1 (ground electronic state with 1 photon) and |e, 0 ≡ |e ⊗ |0 (excited electronic state with 0 photons), through g, 1| μ(â † + â)|e, 0 = µ ge 1|(â † + â)|0 . When the energy of these two states are very close, the |g, 1 and |e, 1 states hybridize, leading to the formation of polariton states. Using such a simple Hamiltonian, it has been shown that the presence of the cavity can suppress or enhance photo-isomerizations, increase charge transfer rates by orders of magnitude, modify potential energy landscapes even with no photon in the cavity, enhance electron-phonon coupling strength, accelerate singlet fission kinetics, remotely control chemical reactions, enhance excitation energy transfer processes, and create new polariton induced conical intersections. All of these emerging features of the polariton chemistry demonstrate a great promise to control and tune chemical reactivities, as the cavity quantum electrodynamics (QED) processes take advantage of the quantum nature of the light and its interaction with the molecular system. Recently, several theoretical works have demonstrated that the ground state of a molecular system can be significantly modified by coupling to a cavity photon mode with a photon frequency in the electronic excitation range. In particular, Ref. 35 demonstrates that the aminopropenal proton transfer reaction barrier can be modified by coupling the system with the cavity. Note that the cavity frequency in these studies is chosen to be in the range of electronic excitation (in terms of energy, a couple of eV), thus different than the recently explored vibrational strong coupling (VSC) regime (in terms of energy, a couple of meV). These modifications are caused by indirect couplings between different photon-dressed states, due to the presence of both transition and permanent dipoles. For example, the |g, 0 state couples with |g, 1 through g, 1| μ(â † + â)|g, 1 = µ gg 1|(â † + â)|0 , and |g, 1 couples to the |e, 0 through µ ge 1|(â † + â)|0 . As such, the |g, 0 and the |e, 0 states are indirectly coupled to each other (through the light-matter interactions), and the ground state properties can also be significantly influenced under the strong light-matter interaction coupling strength. Further, the dipole selfenergy (DSE) term (see Eq. 1, the last term) could also significantly influence the ground state properties and reactivities, as demonstrated in Ref. 35. This is because the DSE operator can be expressed as g| D|e i = λ 2 2 α μgα μαe i where |α ∈ {|g , |e 1 ...|e i ...}. One can clearly see that the DSE term is able to connect electronic adiabatic states far away in energy. However, an intuitive and simple understanding of cavity modification of the molecular ground state is still missing. As such, the cavity-modified chemical reactivity in the ground state is an interesting new direction, but not well understood due to those indirect effects as we mentioned above.