Molecular Polariton Dynamics in Realistic Cavities.

The large number of degrees of freedom involved in polaritonic chemistry processes considerably restricts the systems that can be described by any ab initio approach, due to the resulting high computational cost. Semiclassical methods that treat light classically offer a promising route for overcoming these limitations. In this work, we present a new implementation that combines the numerical propagation of Maxwell's equations to simulate realistic cavities with quantum electron dynamics at the density functional tight-binding (DFTB) theory level. This implementation allows for the simulation of a large number of molecules described at the atomistic level, interacting with cavity modes obtained by numerically solving Maxwell's equations. By mimicking experimental setups, our approach enables the calculation of transmission spectra, in which we observe the corresponding polaritonic signals. In addition, we have access to local information, revealing complex responses of individual molecules that depend on the number, geometry, position, and orientation of the molecules inside the cavity.