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Density-functional based study of nanomaterials: i) vdW interactions between nanocrystals and surfaces, ii) alloying effects in the optical properties of Si-Ge clusters

Authors: S. Botti

Ref.: Seminares du IEMN, Lille, France, 14/3/2008 (2008)

Abstract: Time-dependent density functional theory (TDDFT) allows to study ab-initio the electronic excitations involved in spectroscopic experiments, possibly conserving a computational effort comparable to that of ground-state density functional theory (DFT). For this reason, TDDFT is particularly suitable to treat large scale nanostructures. Here I will present two examples of applications of TDDFT to the calculation of the electronic excitations of nanocrystals. First, I will discuss the ab-initio calculation of van der Waals interactions between nanoclusters and of a nanoscluster on a surface. The methods used are efficient and allow to study systems containing hundreds of atoms. For larger systems, we propose to use simple semi-empirical models with an error smaller than 10%. Second, I will show a study within TDDFT of the composition dependence of the optical properties of SixGe(1-x) nanocrystals. The excitation energies and the Stoke shifts have a distinct non-linear dependence on the composition. The theoretical results are compared with previous independent-particle DFT calculations and experimental luminescence data.

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