Atomistic treatments of electronic relaxation at photoexcited semiconductor surfaces
David A. Micha
Departments of Chemistry and of Physics, Quantum Theory Project, University of Florida Gainesville, Florida 32611, USA
Relaxation times of electrons and holes, created by light absorption at the surface of a semiconductor, are important parameters in the description of photovoltaic and photocatalytic materials. These are more efficient when the photoinduced charge carriers are long lived. Lifetimes of the carriers depend on atomic structures and their lattice dynamics, in addition to their dependence on the wavelength and intensity of absorbed light, and they must be modelled starting from atomistic treatments. This can be done with recent density functionals which generate orbital basis sets for valence and conduction band states of semiconductors, and provide accurate band gaps. The DFT orbital basis sets can be incorporated into theoretical treatments of photoinduced non-adiabatic dynamics by means of ab initio non-adiabatic DFT [1] or using reduced density matrices (RDMs) which account for dissipative and non-adiabatic dynamics. Approaches based on combined DFT/RDM are quite efficient and have been applied to nanostructured surfaces of Si [2] and TiO2 [3] among other materials. This contribution describes how electronic relaxation times can be extracted from (a) direct numerical integration over time of the equation of motion for RDM elements, and from (b) solutions of eigenvalue equations for steady-state RDMs which directly provide relaxing electronic densities [4] while bypassing the need to integrate over time the equations of motion.
[1] R. Long and O. V. Prezhdo, JACS 2014, 136, 4343.
[2] D. S. Kilin and D. A. Micha, Phys. Chem. Letters 2010, 1, 1073
[3] T. Vazhappilly, M. P. deLara-Castells, and D. A. Micha, Mol. Phys. (2018) DOI: 10.1080/00268976.2018.1533651
[4] D. A. Micha, Adv. Quantum Chem. 71, 195 (2015)
Related work has been supported at the University of Florida by the National Science Foundation, Chemistry Division, and by the University of Florida High Performance Computing facility.