posted on 2024-01-08, 14:04authored byMark Kamper Svendsen, Kristian Sommer Thygesen, Angel Rubio, Johannes Flick
The emerging field
of strongly coupled light–matter systems
has drawn significant attention in recent years because of the prospect
of altering both the physical and chemical properties of molecules
and materials. Because this emerging field draws on ideas from both
condensed-matter physics and quantum optics, it has attracted the
attention of theoreticians from both fields. While the former often
employ accurate descriptions of the electronic structure of the matter,
the description of the electromagnetic environment is often oversimplified.
In contrast, the latter often employs sophisticated descriptions of
the electromagnetic environment while using oversimplified few-level
approximations of the electronic structure. Both approaches are problematic
because the oversimplified descriptions of the electronic system are
incapable of describing effects such as light-induced structural changes
in the electronic system, while the oversimplified descriptions of
the electromagnetic environments can lead to unphysical predictions
because the light–matter interactions strengths are misrepresented.
In this work, we overcome these shortcomings and present the first
method which can quantitatively describe both the electronic system
and general electromagnetic environments from first principles. We
realize this by combining macroscopic QED (MQED) with Quantum Electrodynamical
Density-Functional Theory. To exemplify this approach, we consider
the example of an absorbing spherical cavity and study the impact
of different parameters of both the environment and the electronic
system on the transition from weak-to-strong coupling for different
aromatic molecules. As part of this work, we also provide an easy-to-use
tool to calculate the cavity coupling strengths for simple cavity
setups. Our work is a significant step toward parameter-free ab initio calculations for strongly coupled quantum light–matter
systems and will help bridge the gap between theoretical methods and
experiments in the field.