A First Principles Study of Capping Energies and Electronic States in PbSe Nanocrystals
Fabio Grassi a, Maurizio Cossi a, Mario Argeri a, Leonardo Marchese a
a Dipartimento di Scienze ed Innovazione Tecnologica, Viale Teresa Michel n 11 - 15121 Alessandria, Italy
Oral, Fabio Grassi, presentation 025
Publication date: 1st April 2013

 

Semiconductor quantum dots (QDs) are a relatively recent family of materials characterized by a marked dependence of physico-chemical properties on size and morphology. This intrinsic tunability makes them excellent candidates for applications in different fields such as molecular imaging, quantum computing and photovoltaics.

In the present work, PbSe QDs were modelled by extracting clusters of cubic, cuboid, cuboctahedral and octahedral morphology from the cubic PbSe lattice. The effects of ligand adsorption, cluster stoichiometry and morphology on electronic structure have been investigated. Addition energies of different ligands were also calculated. Calculations were performed at DFT level with B3-LYP functional for geometry optimizations and B-LYP for electronic structures, with a modified LANL2DZ basis set with polarization functions for Pb, Se and S and 6-31G** for  all other elements.

Results indicate a strong dependence of electronic structure on cluster stoichiometry, with a 1:1 relationship between intra-band states and the number of excess Pb or Se atoms. Average addition energy of capping molecules to cluster surface has been shown to decrease, albeit irregularly, as the number of adsorbed ligands increases. Ligand-induced removal of intra-band states has been noted to be effective only with certain types of capping species.


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