Research directions focus on the theoretical description and simulation of quantum and classical dynamical phenomena in systems of varying complexity, ranging from solute-solvent systems to photochemically active chromophore-DNA/RNA complexes and semiconducting polymers.
The interplay of quantum dynamical processes with structured and dynamically responding environments poses a considerable challenge. This is particularly manifest in ultrafast excited-state processes where coherent quantum evolution is accompanied by the environment's non-equilibrium dynamics. Our recent work in this context includes the photophysics of functional organic polymer materials, involving exciton decay at donor-acceptor heterojunctions [Huix-Rotllant, Tamura, Burghardt, J. Phys. Chem. Lett. 6, 1702 (2015), Polkehn et al., J. Phys. Chem. Lett. 7, 1327 (2016)] and singlet fission [Tamura, Huix-Rotllant, Burghardt, Olivier, Beljonne, Phys. Rev. Lett. 115, 107401 (2015)].
Hybrid quantum-classical and QM/MM methods, along with classical MD approaches are employed to study photoactive biological assemblies. Recent work has addressed the controlled destabilization of RNA and DNA by azobenzene photoswitches [Mondal, Biswas, Goldau, Heckel, Burghardt, J. Phys. Chem. B 119, 11275 (2015), Rastaedter, Biswas, Burghardt, J. Phys. Chem. B 118, 8478 (2014)].
Method development combines (i) quantum and mixed quantum-classical methods suitable for many dimensions, in particular multiconfigurational methods and trajectory-based methods, with (ii) reduced-dimensional models, for example effective-mode models [Martinazzo, Hughes, Burghardt, Phys. Rev. E 84, 030102(R) (2011)]. Current efforts are directed, in particular, at multiconfigurational Gaussian-based representations in many dimensions [Roemer, Ruckenbauer, Burghardt, J. Chem. Phys. 138, 064106 (2013), Richings et al., Int. Rev. Phys. Chem. 34, 265 (2015)]. A complementary strategy focuses on hybrid approaches involving mesoscopic descriptions like classical Dynamical Density Functional Theory (DDFT) to describe time-evolving nonequilibrium environments interacting with a quantum subsystem [Hughes, Baxter, Bousquet, Ramanathan, Burghardt, J. Chem. Phys. 136, 014102 (2012)].