Igor Vasiliev

Optical Properties of Hydrogenated Silicon Clusters with Reconstructed Surfaces

We study the effects of surface reconstruction on the absorption spectra and optical gaps of hydrogen-terminated silicon clusters. The spectra and gaps are computed using an ab initio method based on the linear response theory within the time-dependent local-density approximation (TDLDA). Our calculations show that the structural reconstruction of cluster surfaces produces new absorption bands in the lower part of the spectrum and causes a significant reduction of the optical gap. The optical gaps in surface-reconstructed silicon clusters appear to be similar in size to those in clusters with partially oxidated surfaces. Our results suggest that both surface oxidation and surface reconstruction are essential to resolve disagreements between the optical gaps measured in experiments and theoretical predictions based on a quantum confinement model.

OPTICAL EXCITATIONS IN NANOSTRUCTURES: APPLICATION OF TIME DEPENDENT DENSITY FUNCTIONAL THEORY TO Sin (n=3-10) CLUSTERS

Determining excited state properties of atomic clusters is a challenging problem. In general, the ground state structural properties of clusters are unknown and not subject to direct experimental probes. Without knowledge of these properties, it is not possible to predict accurate optical excitations in clusters. Here we present a real-space-pseudopotential method to determine the structural properties of Sin clusters via simulated annealing and the corresponding optical properties from the time dependent local density approximation (TDLDA).