Alkali halides happen to be extensively studied due to their necessary
applications in scintillation detectors, photography, medicine and chemical
market. It's also exciting that they may be implemented as prototype systems to
test theoretical models, simply because they belong to compounds typical ironic.
Their structural and electronic properties are the basis to clarify properly
linked optical and electrical phenomena, which are essential for their
applications. On the other hand, few investigations have focused on their
structural properties and density of electronic states. The theory of density
functional has been extensively applied to study the properties with the ground
state of the supplies, which could get the exact parameters with the structure
despite the fact that it usually underestimates the band gap. We currently
employed this process to study the structural and electronic properties of
alkali halides. In this passage, our attention is paid only for sodium bromide
for the reason that it is actually representative for the other, and above all
there's adequate experimental and theoretical information, that are necessary to
verify our outcomes.
All calculations are performed within the DFT-GGA as implemented in the
ABINIT package, which is based on ab initio pseudopotentials along with a basis
set of plane wave. The pseudopotentials applied are generated by the program
Trouiller-Martin, which is included in the code FHI98PP. The valence electrons
for Na and Br are considered and 3s1 4s24p5, respectively. The
Perdew-Burke-Ernzerh (PBE) function is employed to reflect the
exchange-correlation power, along with the strategy of conjugate gradient
minimization algorithms for a self-consistent field (SCF) cycles. Two parameters
that significantly have an effect on the accuracy and time in the calculation
are the cutoff power of plane wave along with the particular k point grid. To
properly pick the two parameters, we initially carry out a series of convergence
tests. In our work, the cutoff energy is 25 Ha for all cases, and also the
particular k points sampling integration more than the Brillouin zone are
employed making use of the Monkhorst-Pack strategy with 6 ??¡ì?¨¦ 6 ??¡ì?¨¦ 6
unique k -point mesh.
Sodium bromide(7647-15-6) belongs to the group Fm-3m space (225) and each
primitive cell contains two atoms with atomic positions of Na+ ions at (0,0,0)
and Br-ions (0.five,0.five,0.5 ). Before calculating the electronic structure,
the optimal geometric structure is produced to locate the equilibrium values of
the lattice constants a. For calculating structural relaxation, we adjust the
lattice constants close towards the declared value, then calculate the total
energy E for unique values ??from the unit cell volume V. The volume of the cell
balancing unit V0, bulk modulus B0 and its pressure derivative B00 (ie, dB / dP)
are obtained by fitting the calculated data towards the third order
Birch-Murnaghan equation of state ( EOS), where E0 and V are the total power
balance plus the volume of unit cell, respectively. It really should be noted
that excellent agreement is obtained on the volume of unit cell varied. The
network equipped continual, bulk modulus, its derivative and pressure are a =
6.02MA, B0 = 193.64 kbar, and B00 = 3.84, respectively. Our calculated worth
from the lattice continual is 0.84% larger than the experimental one particular
(5.97MA). Thomas and Shanker also studied the modulus of the sodium bromide
using the Birch equation of state (BES), which was derived from the theory of
finite deformation. Their results show that B0 and B00 are 199 kbar and 5.46,
respectively. Thus, our result is just about the identical because the
experimental worth of B0 (195 kbar) and much more accurate.
It could be seen that sodium
bromide is direct gap insulator with all the valence band maximum (VBM) and
conduction band minimum (CBM) in theprocess. Our calculated lattice continuous
balance is 0.84% greater than the experimental worth, and also the bulk modulus
and its pressure derivatives are in pretty much the same because the reported
data. The band structures, DOS and PDOS are presented, and outcomes were
discussed and compared with on the market experimental information and
theoretical.
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