A Real-Time Time-Dependent Density Functional Tight-Binding Implementation for Semiclassical Excited State Electron-Nuclear Dynamics and Pump-Probe Spectroscopy Simulations.

The increasing need to simulate the dynamics of photoexcited molecular systems and nanosystems in the subpicosecond regime demands new efficient tools able to describe the quantum nature of matter at a low computational cost. By combining the power of the approximate DFTB method with the semiclassical Ehrenfest method for nuclear-electron dynamics, we have achieved a real-time time-dependent DFTB (TD-DFTB) implementation that fits such requirements. In addition to enabling the study of nuclear motion effects in photoinduced charge transfer processes, our code adds novel features to the realm of static and time-resolved computational spectroscopies.

Trap-Door-Like Irreversible Photoinduced Charge Transfer in a Donor-Acceptor Complex.

For efficient conversion of light into useful energy sources, it is very important to study and describe the first steps of primary charge-transfer process in natural structures and artificial devices. The time scale of these processes in artificial photosynthetic and photovoltaic devices is on the order of femto- to picoseconds and involves vibronic coupling of electrons and nuclei and also nuclear alleviation to enhance charge separation. Here we present an atomistic description of the photoexcited electron dynamics in a noncovalently bonded system formed by an hydrogenated nanodiamond as donor and a perylene diimide as an acceptor.

Photoinduced charge-transfer dynamics simulations in noncovalently bonded molecular aggregates.

The rational design of new materials as prototype systems for organic solar cells remains challenging. Perylene diimide has emerged as a promising material to replace fullerene derivatives because of its synthetic flexibility, leading to the manipulation of their optical properties. As a result of their fused aromatic core that favors π-π stacking interactions, the aggregation of these molecules can reach highly ordered nanostructures as one-dimensional nanofibers, with a fast photoinduced charge transfer mechanism.