Time-dependent density functional theory approximations for charge separation processes

Abstract

The mechanisms that lead to efficient charge separation in donor-acceptor molecular systems are not fully established yet. They might be related to electronic states that are above the charge transfer state or boosted by local dielectric screening. Time-Dependent Density Functional Theory (TDDFT) is an excellent tool to investigate these systems, especially when large multimolecular systems need to be explicitly represented, since it has a reasonable computational cost while yet an exact quantum chemistry theory. However, in practice, the exchange-correlation (xc) energy and associated functionals need to be approximated, incorporating conceptual shortages in the theory when describing charge transfer excitations. We aim to develop TDDFT approximations that are appropriated to deal with these transitions in solvated structures and investigate prominent donor-acceptor molecular systems. This will be done by implementing the ``naturally'' screened Optimally Tuned Range Separated Hybrid (OT-RSH) functional in TDDFT applied to covalent and stacked donor-acceptor associations. The systems will be composed by phenothiazine dyes, S,N-heteroacene, and Naphthalene diimide, also in the presence solvent, ionic liquid and other environments proposed in the main project. Furthermore, we aim to collaborate with the group of Prof. Stephan Kummel on implementing Ehrenfest dynamics in their real-time TDDFT code, and evaluate these donor-acceptor systems in order to understand the importance of nuclear motion in charge separation processes. With these strategies we intend to develop TDDFT approximations that can picture the importance of the molecular environment in charge separation and contribute to define its driving mechanisms. (AU)