How different are Te clusters—a first-principles study

Density functional theory-based electronic structure calculations are carried out to obtain the geometries corresponding to the lowest three energy values for Tey (y = 2 − 20) clusters. A comparison of the stability from binding energy curve of these clusters with exchange-correlation energy functional approximated within the local density approximation (LDA), generalized gradient approximation (GGA) and hybrid functional (PBE0) indicates the structures to be most stable within the LDA, and these results are also found to be closer to those obtained from the experiments. A transition from two-dimensional to three-dimensional structures is observed at y = 5. Clusters form arm-chair and crown-like structures for small sizes and ring-like geometries for larger sizes. Partial charge density and eigenvalue spectrum reveal that there is no s-p hybridization and the highest occupied states are mostly π non-bonding orbitals. Clusters with even number of atoms show a charge distribution approximately uniformly localized around each atom similar to the σs anti-bonding orbital in Te2. Comparative study of the structural and electronic properties of small Tey clusters (y = 2 − 8), with corresponding isoelectronic sulphur and selenium clusters, predicts sulphur clusters to be most stable and Te clusters to be least stable. Bond lengths increase while bond angles decrease in going from S → Se → Te but the shapes of the geometric structures are more or less the same. Following the work of Ghosh et al. (J Phys Chem C 112:983–989, 2008) on Te helical structures and Pal et al. (Sci Rep 3:2051-1-7, 2013) on Se helical chains, we have carried out spin-polarized electronic structure calculations for helical chains of Tey (y = 3 − 8). Interestingly, we have found that Te helical chains also reveal a behaviour similar to that predicted for Se chains by Pal et al.