Chemists have long fantasized about influencing chemical reactivity, creating molecules impossible with the conventional toolset of synthetic chemistry, and unraveling mechanisms of energy transfer relevant to photosynthesis. To this end, I have recently become interested in understanding the role of coupling electronic excitations of a molecule to vacuum modes of optical cavities, creating light-matter hybrids called polaritons that can influence chemical reactivity. In 2012, Thomas et al. re-ignited interest in this field of electronic polariton chemistry when they demonstrated that a chemical reaction, at room temperature, could be modified within the environment of a resonantly-tuned cavity without externally driving the system [Thomas, A. et al. Angew. Commun. 51, 1592 (2012)]. This discovery opened the door to myriad tantalizing possibilities, but despite intense efforts since by scientists around the world to understand why the reaction rate changes, no convincing explanation exists.
I am interested in modeling this cavity-modified chemical reaction from first principles by creating polaritonic potential energy surfaces connected by non-adiabatic coupling elements modified by the light-matter interactions and propagating a nuclear wavepacket along them to see if the change in reaction rate can be reproduced computationally. While polaritonic potential energy surfaces with non-adiabatic coupling elements have previously been constructed and nuclear dynamics have been studied on them, these studies have either used simple parametrized potential energy surfaces [Galego et al. Nat. Commun. 7, 13841 (2016)] or studied only smaller molecules accessible via wavefunction-based electronic structure methods [Fregoni et al. Nat Commun. 9, 4688 (2018); Antoniou et al. J. Phys. Chem. Lett. 11, 9063 (2020)]. All studies, by building the polaritonic potential energy surfaces by coupling the electronic potential energy surfaces to cavity modes with cavity quantum electrodynamics methods, have also neglected to include important light-matter coupling terms, such as the counter-rotating terms and dipole self-energy.
I am interested in using the first-principles-based method quantum electrodynamical density functional theory (QEDFT), which treats quantized electrons and photons on equal footing. Importantly, this method can be more accurate than traditional cavity quantum electrodynamics methods by including all degrees of freedom of the molecule, rather than treating it as a simple N-level system, as well as by including the counter-rotating and dipole self-energy terms. Calculating polaritonic potential energy surfaces with this electron density-based method also has the potential to be faster than approaches based on wave function-based quantum chemistry methods, such as configuration interaction. With these two complementary advantages of being more accurate than cavity quantum electrodynamics methods and faster than wave function-based methods, QEDFT may be a more appropriate tool for studying realistic reactions under electronic strong coupling.
In this project, we would either implement a trajectory surface hopping method with light-matter coupling in QEDFT, which is currently implemented in the real-space DFT software OCTOPUS, or modify an existing implementation of calculating non-adiabatic coupling elements.