Submitted Abstract
Quantum-mechanical nuclear and electronic fluctuations are ubiquitous in a wide range of molecular materials. The complex interplay of nuclear and electronic effects gives rise to a fascinating variety of properties and functions of these materials. Notwithstanding the extensive development of sophisticated models for these individual phenomena in the past, a truly coupled description beyond the widely employed Born-Oppenheimer approximation has not yet been achieved for real-world applications. The main objective of this project is to develop such a combined treatment of both electronic and nuclear quantum-mechanical fluctuations in the context of molecular materials. We intend to do so by non-adiabatically coupling nuclear dynamics to a set of quantum harmonic oscillators, the latter of which has been shown to accurately model electronic fluctuations in the recently developed many-body dispersion scheme. Such a combined model represents a promising route towards capturing the whole range of non-classical effects in molecular systems and can be used to resolve yet undiscovered interdependencies of dynamic electronic fluctuations and nuclear motion. Intrinsic electronic fluctuations also form the basis for van der Waals dispersion interactions (long-range correlation forces), which play a pivotal role in, e.g. biomolecular systems. Hence, van der Waals interactions are inherently quantum-mechanical and many-body in nature, which nevertheless is neglected in state-of-the-art simulations. Using a combined approach of the many-body dispersion formalism and Density-Functional Tight-Binding, we study the role of the collective electronic fluctuations and the quantum-mechanical nature of dispersion interactions for the stability, dynamics, and functionality of biomolecular systems. As such systems are embedded in aqueous environments in nature, this as well involves the investigation of long-range correlation forces in solvated systems.