Investigating quantum confinement in silicon nanocrystals using TD-DFT and GW/BSE Eimear Madden, Martijn Zwijnenburg University College London, UK Silicon nanocrystals are promising materials for various electronic and optoelectronic applications, including solar cells, LEDs, and transistors. Although ground-state theories like Density Functional Theory (DFT) are useful for analysing the ground-state energy and providing initial insights into nanocrystals such as trends in electronic structure with particle size, a thorough understanding of their electronic structure, excitonic properties, and charge transport mechanisms requires inherently excited-state methods such as Time-Dependent Density Functional Theory (TD-DFT), or GW combined with the Bethe-Salpeter Equation (BSE).Such insight can contribute to the design and development of more efficient and optimized nanosilicon-based devices. Furthermore,these advanced, excited-state methods can serve as a validation platform for assessing the reliability of approximate models in explaining the impact of particle size on the electronic and optical characteristics of semiconductors, such as quantum confinement effects. In this work, TD-DFT and GW/BSE were applied to investigate quantum confinement effects in hydrogen capped- silicon nanoclusters of various sizes. The accuracy of the computationally cheaper TD-DFT with the more inherently accurate GW/BSE method was also compared. Following this, the capping hydrogen atoms were substituted with thiol and alkyl ligands to gain a better understanding of potential charge transfer effects between surface ligands and the silicon core. To broaden the scope of this investigation, other promising optoelectronic materials such as gallium-arsenic species will be considered in the future.
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