Alkali halides have been extensively studied due to the fact that of their important applications in scintillation detectors, photography, medicine and chemical industry. It shall also be interesting that they should be used as prototype processes to test theoretical models, due to the fact that they belong to compounds typical ironic. Their structural and electronic properties are the basis to explain correctly associated optical and electrical phenomena, which are important for their applications. However, little investigations have focused on their structural properties and density of electronic states. The theory of density functional was extensively used to learn the properties regarding the ground state regarding the materials, which should get the exact parameters regarding the structure consequently it generally underestimates the band gap.
We already used this method to learn the structural and electronic properties of alkali halides. In this passage, our attention is paid only for sodium bromide due to the fact that it is representative for the other, and above all there is sufficient experimental and theoretical data, which are important to verify our results. All calculations are performed within the DFT-GGA as implemented within the ABINIT package, that is based on ab initio pseudopotentials and a basis set of plane wave. The pseudopotentials used are generated by the system Trouiller-Martin, that is included within the code FHI98PP. The valence electrons for Na and Br are regarded and 3s1 4s24p5, respectively.
The Perdew-Burke-Ernzerh PBE function is used to reflect the exchange-correlation energy, and the method of conjugate gradient minimization algorithms for a self-consistent field SCF cycles. 3 parameters that significantly affect the accuracy and time regarding the calculation are the cutoff life of plane wave and the special k spot grid. To correctly select the 3 parameters, we first perform a series of convergence tests. In our work, the cutoff life is 25 Ha for all cases, and the special k points sampling integration over the Brillouin zone are employed creating use of the Monkhorst-Pack method with seven Seven seven special k -point mesh. Sodium bromide 7647-15-6 belongs to team Fm-3m space 225 and each primitive cell contains 3 atoms with atomic positions of Na+ ions at 0,0,0 and Br-ions 0.
Prior to calculating the electronic structure, the optimal geometric structure is created to retrieve the equilibrium values regarding the lattice constants a. For calculating structural relaxation, we change the lattice constants close to declared value, then calculate the total life E for different values? ?of the unit cell volume V. The volume regarding the cell balancing unit V0, bulk modulus B0 and its compression derivative B00 ie, dB or dP are obtained by fitting the calculated data to third order Birch-Murnaghan equation of state EOS, where E0 and V are the total life balance and the volume of unit cell, respectively. It should be noted that good agreement is obtained on the volume of unit cell varied. The network equipped constant, bulk modulus, its derivative and compression are a = 6.
Our calculated cost regarding the lattice constant is 0. 84% larger than the experimental one 5. Thomas and Shanker also studied the modulus regarding the sodium bromide creating use of the Birch equation of state BES, which was derived from the theory of finite deformation. Their conclusions display that B0 and B00 are 199 kbar and 5. Therefore, our result is almost similar as the experimental cost of B0 195 kbar and more accurate.
It shall be seen that sodium bromide is direct gap insulator with the valence band maximum VBM and conduction band minimum CBM within the gamma point. In summary, we studied the structural and electronic properties of sodium bromide by DFT-GGA method. Our calculated lattice constant balance is 0. 84% higher than the experimental value, and the bulk modulus and its compression derivatives are in almost similar as the reported data. The band structures, DOS and PDOS are presented, and conclusions were discussed and compared with available experimental data and theoretical.
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