Abstract
In recent years tremendous progress in the field of light–matter interactions has unveiled that strong coupling to the modes of an optical cavity can alter chemistry even at room temperature. Despite these impressive advances, many fundamental questions of chemistry in cavities remain unanswered. This is also due to a lack of exact results that can be used to validate and benchmark approximate approaches. In this work we provide such reference calculations from exact diagonalization of the Pauli–Fierz Hamiltonian in the long-wavelength limit with an effective cavity mode. This allows us to investigate the reliability of the ubiquitous Jaynes–Cummings model not only for electronic but also for the case of ro-vibrational transitions. We demonstrate how the commonly ignored thermal velocity of charged molecular systems can influence chemical properties while leaving the spectra invariant. Furthermore, we show the emergence of new bound polaritonic states beyond the dissociation energy limit.
Highlights
In recent years tremendous progress in the field of light−matter interactions has unveiled that strong coupling to the modes of an optical cavity can alter chemistry even at room temperature
The basic principles of cavity-modified chemistry are still under debate.[4,16−21] Currently, much of our understanding is based on quantum-optical models that have been designed for single atomic systems, whereas approximate first-principles simulations for coupled matter−photon situations emerge only slowly.[15,22−29] We believe it is pivotal to validate these model approaches and approximate first-principles simulations with numerically exact reference calculations to obtain a detailed understanding of cavity-modified chemistry and to see the limits of the different approximations used
We highlight that the inclusion of the quantized photons makes the interpretation of the obtained spectra much richer and more involved; we discuss the level of accuracy of the ubiquitous Jaynes−Cummings model and demonstrate fundamental effects beyond this model, such as the formation of bound states beyond the dissociation energy limit as well as the influence of the thermal velocity for charged systems
Summary
While the Pauli−Fierz quantum theory as well as nonrelativistic quantum mechanics are not relativistically covariant, for equilibrium properties (the focus of this work) and low-energy processes these theories have been proven to be highly accurate.[4]. Mpt photon modes with frequency ωα are coupled to the matter with the coupling λα that contains the polarization vector and coupling strength of the individual modes. These couplings and frequencies are determined by the properties of the cavity. In the current work we will choose N = 3 and consider the standard case of a single-mode cavity, i.e. Mpt = 1, with polarization in the z direction (see Figure 1).
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