Electronic and Structural Study of Zn_xS_x [x = 12, 16, 24, 28, 36, 48, 96, and 108] Cage Structures

We present a density functional study on the structural and electronic properties of ZnS bubble clusters, specifically, hollow cages whose spontaneous formation was previously observed in classical molecular dynamics simulations by Spano et al. [J. Phys. Chem. B 2003, 107, 10337]. The hollow ZnS cages in our study were modeled as Zn_xS_x [x = 12, 16, 24, 28, 36, 48, 108], and an onionlike structure was modeled as Zn₉₆S₉₆. The study of energetics and stability, performed using large polarized Gaussian basis sets, indicated all structures to be energetically stable with similar binding energy of 5.5-5.6 eV per ZnS pair. Further computation of electronic properties showed that these cages have large vertical ionization energies and relatively low electron affinities in the ranges of 6.8-8.1 and 1.7-3.0 eV, respectively. They have large highest occupied molecular orbital-lowest unoccupied molecular orbital gaps between 2.5 and 3.3 eV, and quasi-particle gaps vary from 6.2 eV for Zn₁₂S₁₂ to 4.19 for Zn₁₀₈S₁₀₈. The computed vibrational frequencies for selected cages, that is, Zn₁₂S₁₂, Zn₁₆S₁₆, Zn₂₈S₂₈ (O, S₄, and S₈ point groups), and Zn₃₆S₃₆ indicate that these cage structures correspond to local minima on the potential energy surface. Finally, the infrared spectra calculated using large basis sets are also reported.