Ab-Initio Calculations of the Vibrational Properties and Dynamical Processes in Semiconductor Nanostructures

The computational facility made available to us in the year 2014 at the High Performance Computing Center Stuttgart (HLRS), enabled us to calculate the lattice strains, the vibrational properties, and carrier relaxation processes in colloidal semiconductor nanoclusters based on first-principles density functional theory (DFT). In this reporting period, we made two important contributions to the field by pushing the boundary in terms of computational power and in term of new algorithmic developments. We studied the phonon-assisted carrier relaxation processes in colloidal semiconductor nanoclusters using large-scale ab initio calculations and found two relaxation pathways for fast carrier relaxation. We also studied the strains and their consequences on the vibrational properties in colloidal semiconductor core-shell nanoclusters. We found a heavily compressive strain on both the cores and the shells of InAs-InP and CdSe-CdS core-shell nanoclusters, which contributes a large blue-shift of the vibrational frequencies. These results lead to a different interpretation of the frequency shifts of recent Raman experiments.