First Principles Simulation of Excited Charge Carrier Dynamics and Role of Decoherence

A greater understanding of excited charge carrier dynamics in materials is fundamental to improving various technological applications. Although rapid advancements have been made in this area, many questions still remain on how changes to the structural details of the materials at the atomistic level affect such quantum dynamics. The fewest-switches surface hopping (FSSH) algorithm together with first-principles dynamics simulations provide us with a predictive approach to simulate such phenomena. However, the FSSH method fails to take into account decoherence effects in the simulations and the extent to which decoherence affects excited carrier dynamics remains unclear. Thus, in this thesis work, we investigate the excited carrier dynamics in a few materials using first-principles simulations with decoherence correction in the FSSH simulation. For our study on the size dependence and role of decoherence in hot electron relaxation within fluorinated silicon quantum dots, the shuttling behavior of hot electron observed in the smaller quantum dot was absent in the case of the larger quantum dot. Decoherence was found to slow down hot electron relaxation by as much as a factor of two. In our work on the excited electron dynamics at the interface of a quantum dot and molecule, excited electron transfer from quantum dot to molecular HOMO was significantly slowed down by more than an order of magnitude by decoherence although for the case of excited electron relaxation the slow down remains around a factor of two. Finally, we examined the excited hole relaxation in a DNA molecule generated via ion irradiation. Excited hole relaxation was found to depend significantly on the energetic position of the generated hole. However, the initial holes in different spatial moieties such as nucleotide bases or phosphate backbones did not show noticeable differences in relaxation time. Decoherence slows down relaxation by a factor of two or more but the relaxation time was found to be much shorter than the typical timescales associated with chemical bond formation/dissociation.Doctor of Philosoph