Ab-Initio Vibro-Polaritonic Spectra in Strongly Coupled Cavity-Molecule Systems

Recent experiments have revealed the profound effect of strong light-matter interactions in optical cavities on the electronic ground state of molecular systems. This phenomenon, known as vibrational strong coupling (VSC), can modify reaction rates and induce the formation of molecular vibrational polaritons, hybrid states involving both photon modes and vibrational modes of molecules. We present an ab-initio methodology, based on the cavity Born-Oppenheimer Hartree-Fock ansatz, which is specifically powerful for ensembles of molecules, to calculate vibro-polaritonic IR spectra. This method allows a comprehensive analysis of these hybrid states. Our semi-classical approach, validated against full quantum simulations, reproduces key features of the vibro-polaritonic spectra. The underlying analytic gradients also pave the way for optimizing cavity-coupled molecular systems and performing semi-classical dynamics simulation

Cavity-Born-Oppenheimer Hartree-Fock Ansatz: Light-matter Properties of Strongly Coupled Molecular Ensembles

Experimental studies indicate that optical cavities can affect chemical reactions, through either vibrational or electronic strong coupling and the quantized cavity modes. However, the current understanding of the interplay between molecules and confined light modes is incomplete. Accurate theoretical models, that take into account inter-molecular interactions to describe ensembles, are therefore essential to understand the mechanisms governing polaritonic chemistry. We present an ab-initio Hartree-Fock ansatz in the framework of the cavity Born-Oppenheimer approximation and study molecules strongly interacting with an optical cavity. This ansatz provides a non-perturbative, self-consistent description of strongly coupled molecular ensembles taking into account the cavity-mediated dipole self-energy contributions. To demonstrate the capability of the cavity Born-Oppenheimer Hartree-Fock ansatz, we study the collective effects in ensembles of strongly coupled diatomic hydrogen fluoride molecules. Our results highlight the importance of the cavity-mediated inter-molecular dipole-dipole interactions, which lead to energetic changes of individual molecules in the coupled ensemble

Unraveling a cavity induced molecular polarization mechanism from collective vibrational strong coupling

We demonstrate that collective vibrational strong coupling of molecules in thermal equilibrium can give rise to significant local electronic polarization effects in the thermodynamic limit. We do so by first showing that the full non-relativistic Pauli-Fierz problem of an ensemble of strongly-coupled molecules in the dilute-gas limit reduces in the cavity Born-Oppenheimer to a cavity-Hartree equation. Consequently, each molecule experiences a self-consistent coupling to the dipoles of all other molecules. In the thermodynamic limit, the sum of all molecular dipoles constitutes the macroscopic polarization field and the self-consistency then accounts for the delicate back-action on its heterogeneous microscopic constituents. The here derived cavity-Hartree equations allow for a computationally efficient implementation in an ab-initio molecular dynamics setting. For a randomly oriented ensemble of slowly rotating model molecules, we observe a red shift of the cavity resonance due to the polarization field, which is in agreement with experiments. We then demonstrate that the back-action on the local polarization takes a non-negligible value in the thermodynamic limit and hence the collective vibrational strong coupling can modify individual molecular properties locally. This is not the case, however, for dilute atomic ensembles, where room temperature does not induce any disorder and local polarization effects are absent. Our findings suggest that the thorough understanding of polaritonic chemistry, e.g. modified chemical reactions, requires self-consistent treatment of the cavity induced polarization and the usually applied restrictions to the displacement field effects may be insufficient

An RNA Aptamer that Induces Transcription

We identified an RNA aptamer that induces TetR-controlled gene expression in Escherichia coli when expressed in the cell. The aptamer was found by a combined approach of in vitro selection for TetR binding and in vivo screening for TetR induction. The smallest active aptamer folds into a stem-loop with an internal loop interrupting the stem. Mutational analysis in vivo and in-line probing in vitro reveal this loop to be the protein binding site. The TetR-inducing activity of the aptamer directly correlates with its stability and the best construct is as efficient as the natural inducer tetracycline. Because of its small size, high induction efficiency, and the stability of the TetR aptamer under in vivo conditions, it is well suited to be an alternative RNA-based inducer of TetR-controlled gene expression