Theory of Polaritonic Chemistry

Abstract

In the previous chapter we embraced the complexity of organic molecules by including arbitrary PES in our description of strong coupling with the aim of building a general theory of polaritonic chemistry. In this chapter we generalize these results and analyze the approach of PoPES. We study the general light–matter Hamiltonian from the point of view presented in Chap. 3, i.e., by separating the electronic and photonic DoF from the nuclear coordinates. In Sect. 4.2 we explicitly analyze this in a complete and general way, also presenting a conceptual molecular energy landscape that presents some kind of excited-state process that can be strongly influenced in strong coupling. Then, in Sect. 4.3 we present the potential of the PoPES picture for describing collective phenomena. We show how we can use the spin operators used in the Tavis–Cummings model (see Sect. 2.3) to understand such a complex system. The ensemble of N molecules is formally identical to a single “supermolecule” that encompass the internal DoF of all molecules. This immediately leads to novel phenomena such as the collective protection effect and collective conical intersections, both discussed in detail in this section.