Pathways of Growth of CdSe Nanocrystals from Nucleant (CdSe)₃₄ Clusters

The initial steps in the growth of quantum platelets from the wurtzite-type (CdSe)₃₄ clusters are simulated using density functional theory with the generalized gradient approximation. The nucleant (CdSe)₃₄ cluster has been chosen for simulations because it has experimentally been found to be a magic-size nucleant for the low-temperature growth of CdSe quantum platelets. According to the results of our calculations, the growth is anisotropic and favors the (0001) direction, which is consistent with the experimental findings. We found that growth in other directions lowers the symmetry of the resulting clusters and that the asymmetrical positioning of rhombic defects causes the growing platelet to bend due to the surface strain, which appears to be the limiting factor of growth. An alternative pathway to quantum platelet growth could proceed via the decomposition of (CdSe)₃₄ to (CdSe)₁₃ in electron-donating media, which was found to be thermodynamically favorable. Side product (CdSe)₂₁ generated in this process is capable of growing via hexagonal stacking as well as propagating as a nanotube

Structure and Electronic Properties of Neutral and Negatively Charged RhB_<i>n</i> Clusters (<i>n</i> = 3–10): A Density Functional Theory Study

The geometrical structure and electronic properties of the neutral RhB_<i>n</i> and singly negatively charged RhB_<i>n</i>^– clusters are obtained in the range of 3 ≤ <i>n</i> ≤ 10 using the unbiased CALYPSO structure search method and density functional theory (DFT). A combination of the PBE0 functional and the def2-TZVP basis set is used for determining global minima on potential energy surfaces of the Rh-doped B_<i>n</i> clusters. The photoelectron spectra of the anions are simulated using the time-dependent density functional theory (TD-DFT) method. Good agreement between our simulated and experimentally obtained photoelectron spectra for RhB₉^– provides support to the validity of our theoretical method. The relative stabilities of the ground-state RhB_<i>n</i> and RhB_<i>n</i>^– clusters are estimated using the calculated binding energies, second-order total energy differences, and HOMO–LUMO gaps. It is found that RhB₇ and RhB₈^– are the most stable species in the neutral and anionic series, respectively. The chemical bonding analysis reveals that the RhB₈^–cluster possesses two sets of delocalized σ and π bonds. In both cases, the Hückel 4<i>N</i> + 2 rule is fulfilled and this cluster possesses both σ and π aromaticities