Coupling molecules to an optical cavity can also create a new type of conical intersection (CI), which is referred to as the polariton-induced conical intersection (PICI). Conical intersections in general arise when the separation between adiabatic electronic surfaces goes to zero at a particular nuclear configuration, causing a degeneracy (which appears as a cone type of structure). The cavity photon mode and the molecule are coupled through the λ • μ term in Eq. 104, which characterizes the light-matter coupling vector oriented in the direction of the cavity polarization unit vector ê. We denote the angle between the dipole vector μ and ê as θ (not to be confused with the incident angle in the Fabry-Pérot cavity illustrated in Fig. ), and μ = | μ|, hence the light-matter coupling can be expressed as