Calculation of Cohesive Energies of 3-D Bismuth Selenide (Bi2Se3) and Bismuth Antimony BiSb Topological Insulators: DFT Study

The cohesive energies of 3-dimensional (3-D) topological insulators bismuth antimony (BiSb) and bismuth selenide (Bi2Se3) were calculated. The Fritz Haber Institute Ab-initio molecular simulations (FHI-aims) code was employed for this calculation.  The output files of the FHI-aims code were used during the computation and the total energies at each number of iterations for single free atoms and bulk were then calculated. The results from this work revealed that bismuth atom becomes stable at 3rd iteration meanwhile both selenium and antimony atoms gain stability at the 5th iteration. The results also showed that bismuth antimony acquire stability at the 3rd iteration and bismuth selenide gain stability at 9th iteration. This implies that among the free atoms studied in this work bismuth atom is more stable and for the bulk bismuth antimony is more stable. The cohesive energies of BiSb and Bi2Se3 were calculated using the optimized parameters. The results obtained from the calculation of the cohesive energies in this work were 1.02eV and 1.76eV for BiSb and Bi2Se3 respectively. This results compared reasonably well with experimental results and have little percentage errors of 1.30% for bismuth antimony and 29.55% for bismuth selenide. The deviation observed in this work may be due to the DFT calculation of the solid rather than the atoms themselves.