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PbS Clusters Embedded in Sodalite Zeolite Cavities of Different Compositions: Unraveling the Structural Evolution and Optical Properties Using ab Initio Calculations

Grajciar, Lukáš
The Journal of Physical Chemistry C 2016 v.120 no.47 pp. 27050-27065
adsorption, algorithms, cations, electrostatic interactions, gases, isomers, optical properties, prediction, quantum dots, zeolites
The structure and properties of the PbS quantum dots (QDs) encapsulated in the zeolite host, a system reported to exhibit extremely high nonlinear optical properties, were determined employing a combination of a robust structure prediction tool based on genetic algorithm approach and density functional calculations (DFT) including state-of-the-art two component time-dependent DFT implementation for hybrid exchange correlation functionals. Sizable changes in cluster structures and even isomer stability ordering are observed either with respect to the gas phase or as a result of the change of the sodalite zeolite composition (extra-framework cations and Si:Al ratio). The presence of very small clusters in the zeolite cavities such as monomers or dimers is predicted which are stabilized mostly via dispersion and to lesser extent electrostatic interaction with the host. The optical excitations of the PbS-zeolite composite are confined mostly to the QDs, i.e., the zeolite can be regarded as a confining dielectric matrix that only modulates the optically active states of the PbS QDs. These findings are corroborated by a very good agreement between calculated and experimental optical adsorption spectra, although sizable computational effort is needed as inclusion of relativistic effects (spin–orbit coupling) is essential for proper assignment of the adsorption bands.