Semiconductor quantum dots have a wide variety of applications due to their tunable properties depending on composition, size and surface terminations. Recently a series of atomically precise, pyramid-shaped CdSe quantum dots have been synthesized with the inorganic core structures solved by the atomic pair distribution function (PDF) technique [1]. In this work, we have investigated structural and optoelectronic properties of the synthesized clusters, by combining first-principles DFT and TDDFT calculations with experimental NMR spectra, UV-vis absorbance spectra and PDF analysis. In particular, we systematically examined the adsorption motifs and binding strength of the passivating ligands on the CdSe(315nm) cluster, as well as their influence on energetic stability, core structure and electronic properties of the cluster. Two stable ligand shell arrangements, which differ in the intermolecular hydrogen bonding network, were found to yield most stable structures and satisfy the electron counting rule (ECR) of the inorganic core. It was also found that the core structure and the HOMO-LUMO gap are only slightly influenced by replacing the ligands with pseudo-hydrogen atoms with fractional nuclei charges, provided that the same ECR is applied. A similar scheme was then used to passivate other three clusters in the series and overall an excellent agreement was found between the computed TDDFT optical gaps and the measured ones.  Such an approach provides an accurate and convenient means for probing the core structure and optoelectronic properties of semiconductor clusters, without involving the structurally complex ligands. [1] �Structural determination of molecular cadmium selenide quantum dots using pair distribution function analysis�, A. N. Beecher, X. Yang, P. Juhas, A. Lagrassa1, S. J. L. Billinge, J. S. Owen, submitted.

Structural and optoelectronic properties of pyramid-shaped cadmium selenide quantum dots from first-principles calculations

247th National Meeting (2014)

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