A DFT study of Se(n)Te(n) clusters

First principles calculations have been performed to study the characteristic properties of Se(n)Te(n) (n = 5–10) clusters. The present study reveals that the properties of these small clusters are consistent with the properties of Se–Te glassy systems. Several hundred equilibrium structures obtained from a genetic algorithm based USPEX code are relaxed to their minimum energy using the VASP code. Most of the lowest energy buckled ring-like structures are formed from Se–Te heteropolar bonds. Detailed structural analysis and distance energy plots unveil that many equilibrium structures are close in energy to their global minimum. The computed Raman and IR spectra show the dominance of Se–Te heteropolar bonds, consistent with earlier simulation and experimental findings in Se(1−x)Te(x) glass materials. Low frequency vibrational modes observed in small clusters are characteristic features of amorphous materials. Non-bonding orbitals (lone pair) are observed in the HOMO, whereas the LUMO is formed from purely antibonding orbitals. The dielectric functions corroborate the bonding mechanism and slightly polar nature of Se(n)Te(n) clusters. The energy loss and absorption coefficient indicate the presence of π–plasmons in the UV-visible region. Furthermore, it is ascertained that the use of a hybrid functional (B3LYP) does not affect the properties of small clusters appreciably, except causing a blue shift in the optical spectra. Hence, we find that the small clusters have bearing on the formation of glassy Se–Te systems.