Tunable electronic structure and structural transition of GaAs clusters at high pressure and temperature
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In this study, the electronic structure and structural transition of the GaAs clusters with different compositions were examined by quantum chemical calculations for the first time. The GaAs clusters exhibit highly interesting structural and electronic properties as a function of composition, temperature, and pressure. The phase transitions were observed from the zinc blende structure (P (4) over bar 3m) to the triclinic (P (1) over bar) and the tetragonal (P (4) over bar) structure where there are two and four intermediate phases, respectively. The As-rich clusters are generally more stable than that of the Ga-rich. The HOMO, LUMO and gap energies, Fermi levels, dipole moments and density of states were analyzed. The gap energy for the Ga8As32 cluster was predicted as about 1.22 eV wide, i.e., about 0.29 eV smaller than the measured band gap of bulk Ga-0.5 As(0.5 )1.51 eV at T = 0 K, while the gap energy for the Ga32As8 is found to be 0.15 eV. The Ga8As32 and Ga32As8 clusters show semiconductor characters with high and low band energy at different pressures, while the Ga32As8 cluster shows metallic character under heat treatment. The trend of energy gap of the clusters is also compatible with available experimental findings. (C) 2019 Elsevier B.V. All rights reserved.