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Quantum chemistry of quantum dots: Effects of ligands and oxidation
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View: Figures


Image of FIG. 1.
FIG. 1.

The three rows correspond to unrelaxed, relaxed, and oxidized by attachment of extra oxygen atom wurtzite structures of , , 15, and 17. For three different cases for relaxed QDs are presented: (a) is relaxed wurtzite-derived QD while (b) and (c) were obtained by reoptimization of oxidized structures (d) and (e) after detachment of oxygen atom. QDs (d) and (e) were obtained by attachment of extra oxygen to three- and two-coordinated Cd atoms, respectively. Structure (b) could also be obtained by sequential substitution of Se atom by O and backward with structure relaxation on each step. Cd is white, Se is yellow, and O is red. The optimized ligated structures cannot be clearly seen because of the hindering effect of the ligands. After the ligands are removed for clarity, they are indistinguishable from unrelaxed structures shown in the top row.

Image of FIG. 2.
FIG. 2.

Linear absorption spectra for unligated, oxidized, and ligated cadmium selenide QDs. For the closed atomic shell structures QD6 and QD17, the removal of the ligands does not change the absorption spectra, while oxidation generates an absorption band close to 800 nm. The unstable unligated isomer QD15a reveals absorption spectrum strongly shifted into the infrared region. Oxidation leads to the reconstruction of QD’s structure and a blueshift in adsorption spectra for and . Reduction in oxidized nanoparticles is accompanied by further blueshift for and relative to the QD with similar topology. Saturation of the dangling bonds of wurtzite-derived QD15 by ligands stabilizes it with calculated absorption spectrum close to the most stable modification with threefold coordinated surface atoms.

Image of FIG. 3.
FIG. 3.

Contour plots calculated for the highest occupied (bottom) and lowest unoccupied (top) one-electron states in (left) and (right) clusters. The unoccupied state in has antibonding character with respect to the oxygen-selenium interaction. It narrows the bandgap to the value of 1.923 vs 2.661 eV bandgap for . Energy levels for HOMO are equal to −6.257 and −5.569 eV, while for LUMO they are −3.596 eV and −3.646 eV for and QDs, respectively.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Quantum chemistry of quantum dots: Effects of ligands and oxidation