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Structural, elastic, optoelectronic and optical properties of CuX (X= F, Cl, Br, I): A DFT study

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The structural, elastic, electronic and optical properties of copper halides CuX (X= F, Cl, Br, I) are performed by using the full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). The exchange correlation potential was described by generalized gradient approximation (GGA) and Engel-Vosko generalized gradient approximation (EV-GGA). For better electronic properties we have used the modified Becke–Johnson (mBJ) potential. Copper Halides, CuX (X= F, Cl, Br, I) have zinc-blend structure (B3) and shows direct band gap. The results obtained for band structure using mBJ potential shows a significant improvement over previous theoretical work and gives closer values to the experimental available data. The elastic constants values have also been analyzed for these materials. In the elastic constants it has been found that CuF and CuBr show brittle nature while CuCl and CuI show ductile behaviour. Optical parameters, like the dielectric constant, refractive indices, reflectivity, optical conductivity and absorption coefficient has also been calculated and presented.
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JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS Vol. 16, No. 11-12, November December 2014, p. 1493 - 1502
Structural, elastic, optoelectronic and optical properties
of CuX (X= F, Cl, Br, I): A DFT study
HAMID ULLAH*,a, A. H. RESHAKb,c, KALSOOM INAYATa , R. ALIa, G. MURTAZAd, SHERAZe, S. A. KHANf, H.
U. DINf, Z. A. ALAHMEDg
aDepartment of Physics, Government Post Graduate Jahanzeb College, Saidu Sharif Swat, Pakistan
bNew Technologies - Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen, Czech Republic
cCenter of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis,
01007 Kangar, Perlis, Malaysia
dDepartment of Physics, Material Modeling Lab, Isalmia College University Peshawer, Pakistan
eDepartment of Physics, Balochistan University of information technology ,engineering and management sciences ,
Pakistan
fDepartment of Physics, Hazara University Mansehra, Pakistan
gDepartment of Physics and Astronomy, King Saud University, Riyadh 11451, Saudi Arabia
The structural, elastic, electronic and optical properties of copper halides CuX (X= F, Cl, Br, I) are performed by using the
full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). The exchange
correlation potential was described by generalized gradient approximation (GGA) and Engel-Vosko generalized gradient
approximation (EV-GGA). For better electronic properties we have used the modified BeckeJohnson (mBJ) potential.
Copper Halides, CuX (X= F, Cl, Br, I) have zinc-blend structure (B3) and shows direct band gap. The results obtained for
band structure using mBJ potential shows a significant improvement over previous theoretical work and gives closer values
to the experimental available data. The elastic constants values have also been analyzed for these materials. In the elastic
constants it has been found that CuF and CuBr show brittle nature while CuCl and CuI show ductile behaviour. Optical
parameters, like the dielectric constant, refractive indices, reflectivity, optical conductivity and absorption coefficient has also
been calculated and presented.
(Received December 26, 2013; accepted November 13, 2014)
Keywords: DFT, mBJ potential, Elastic, optoelectronic, Optical properties
1. Introduction
Copper halides have been studied for several decades
[1-3] but the importance of IB-VIIA semiconductors are
still growing because of the potential applications
occurring from the restricted excitons in micro-crystals
made of these materials [4]. The copper halides crystallize
in the zinc blend lattice (space group F-43m) and are
tetrahedral coordinated semiconductors. Cu atom is
located at position (0, 0, 0), while X (F, Cl, Br, I) atoms
are located at (1/4, 1/4, 1/4) positions. The electronic
configuration of zinc blend structure is derived from sp3-
sp3 configuration while the valence bands of copper
halides are due to sp3-sd3. As a result of the p-d
hybridization considerably changes physical properties of
copper halides are considerably different compared with
other members of ANB8-N series. B. Amrani et al [5]
performed under pressure calculations on these materials
and found that they transform from the zinc-blend (B3) to
the rocksalt (B1) structure. Experimental studies [6-8]
have revealed that CuCl, CuBr and CuI adopt the rocksalt
structure at a pressure around in the region of 10 GPa,
though the zinc blende-rocksalt transition occurs via
several intermediate structures of lower symmetry.
According to Amrani et al, the most interesting feature of
the copper halides is the occurrence of a filled d10-shell.
The d-electrons in the copper and silver halides are part of
the uppermost valence bands and, therefore, influence the
electronic properties of these compounds. The IVII
semiconductors exhibit nonlinear optical properties. These
materials are promising candidates for photosensitive and
semiconducting materials, hence attract much attention.
A wide range of theoretical studies have been
executed on copper halides. The commonly used pseudo-
potential method made less useful for the calculation of
the energy bands of normal zinc blend semiconductors by
the presence of d levels. The tight binding method was
used to perform the calculation of IB-VIIA compounds by
Song [9] and Khan [10]. The mixed tight binding plane
wave (MTB-PW) calculation were made by Calabrese and
Fowler [11] which have been critically reviewed by
Goldman [12], Zunger and Cohen [13], Kleinman and
Medinck [14] and Kunz and Weidman [15]. Furthermore
calculation had been done by the linear muffin-tin orbital
(LMTO) method [16,17]. The calculations for IB-VIIA
compounds among available pseudo-potential by Wang et
al. [18], Smith [19] and Hsueh et al. [20]. Despite from
numerous theoretical work, the detail are still incomplete
because the predicted band gaps are still much lower than
the experimental measurements. Therefore, it is necessary
to investigate the physical properties of copper halides in
detail.
1494 Hamid Ullah, A. H. Reshak, Kalsoom inayat , R.Ali, G. Murtaza, Sheraz, S. A. Khan, H. U. Din, Z. A. Alahmed
To calculate the band structure of comparatively
localized d valence electron, it is most suitable to use
method which stresses the atomic nature of the wave
function. The objective of this paper is to apply the full-
potential linearized augmented plane wave (FP-LAPW)
method [21] for calculating the structural, elastic,
electronic and optical properties of CuX (X= F, Cl, Br, I).
We have presented here the structural, elastic,
electronic and optical properties for CuX (X= F, Cl, Br, I).
Our calculated values for the structural and electronic
properties for these materials are much better than the
previous work and are very closer to the experimental
results. Here in this work we have included Copper
fluoride (CuF) and to the best of our knowledge there is no
previous work has been done upon it, which can be use as
a reference for future investigations. We have also
calculated the elastic constants values along with Young’s
modulus E (in GPa), shear modulus G (in GPa), Poisson’s
ratio ν, anisotropy factor A and B/G ratio which has not
been done may not be done before this. We have also
calculated the electron density, which is an important
bonding property for a material.
2. Computational details
The calculations are carried out by using the FP-
LAPW [21] method as implemented in Wien2k package
[22]. The exchange correlation potential was described by
generalized gradient approximation of Wu and Cohen
(WC-GGA) [23], Engel and Vosko (EV-GGA) [24-44],
and modified Becke-Johnson potential (mBJ) [17]
potential for the better electronic properties. The last two
approximations are used to overcome the well-known
GGA underestimation of the energy band gap. The
spherical harmonics inside non-overlapping muffin-tin
(MT) spheres surroundings the atomic spheres are
expanded up to lmax= 9. The plane wave cut-off of
RMTKmax = 8.5, was chosen for the expansion of wave
functions in the interstitial region. Meshes of 1000 k-
points are used for the irreducible wedge of Brillouin zone
(BZ). The self-consistent calculations are converged since
the total energy of the system is stable within 10-3Ry.
3. Results and discussions
3.1. Ground state properties
The calculated total energy of CuX (X=F,Cl, Br, I)
unit cell is a function of volume in zinc blend phase. To
calculate the ground state properties of CuX (X= F, Cl, Br,
I), the volume was optimized by the Murnaghan equation
of states [25]. The equilibrium volume, bulk modulus,
derivative of the bulk modulus with some theoretical and
experimental results is given in Table 1. It is clear from the
previous work that both of the local density approximation
(LDA) and GGA underestimate the lattice parameters
while our calculated results using EV-GGA and mBJ are
in good agreement with the experimental data and other
calculated results. From lower to higher atomic number
the bulk modulus and energy decreases, while the lattice
constants increases as we move from CuF to CuI for zinc
blend phase.
Table 1. Calculated ground state properties of CuX (X= F, Cl, Br, I) using mBJ along with experimental and other
theoretical work.
Compounds
Properties
Present Calculation
Experimental
Other Work
EV-GGA
mBJ
LDA/GGA
CuF
ao
4.87
4.77
-
-
Eo
-3510.71
-3506.5191
-
-
B
77.75
78.56
-
-
B/
7.070
5.11
-
-
CuCl
ao
5.45
5.324
5.424b
5.246a, 5.273b
Eo
-4234.25
-4229.1
B
49.5727
63.2804
38.1b,39.8c 54.5d
48.38a
B/
5.00
5.00
4b
5.196a
CuBr
ao
5.76
5.6215
5.695b
5.744a, 5.689i
Eo
-8525.25
-8517.2
B
42.6095
54.8466
36.6b
43.528a
B/
5.00
5.00
4b
5.1a
CuI
ao
6.11
5.965
6.054b
5.885a, 6.082j
Eo
-7550.95
-17540
B
44.6988
40.1147
36.6b, 31e
39.447a
B/
5.00
5.00
4b
4.704a
a[5], b[26], c[27], d[28], e[29], h[20], i[30], j[1]
3.1.1 Elastic properties
The crystal properties like dynamical and mechanical
properties are explained easily by elastic constants; it
explicates material properties under stress i.e when
deformation is produced in its shape and then regains its
original shape after releasing stress [31]. Some valuable
information like stability and stiffness of a material are
Structural, elastic, optoelectronic and optical properties of CuX (X= F, Cl, Br, I): A DFT study 1495
easily explained through this phenomenon. We have used
ab-initio method for the calculation of the elastic moduli
(Cij) by calculating stress tensor components for small
strains, using Charpin’s method implemented in the
WIEN2K simulation package. We have calculated
independent elastic parameters, C11, C12 and C44 for the
complete explanation of mechanical properties of CuX
(X= F, Cl, Br, I) in the zinc blend (B3) phase.
Table 2 clarifies that the unidirectional elastic
constant C11 are higher than that of C44 in zinc blend phase
performed with WC-GGA potential. This shows that
material having larger difference C11-C44 presents a weaker
resistance to the pure shear deformation. In a cubic
structures the condition for mechanical stability leads to
the following reaction on elastic constants [31]:
(1/3) (C11+2C12 >0; C44>0: (C11-C12) >0 (1)
Hence the mechanical condition for these materials
are fulfilled and presenting the elastic stability of these
compounds.
In engineering sciences, elastic anisotropy of a
material play a vital role, it has the possibility to detect
micro-cracks in a material [32] due to high correlativity.
The anisotropy factor A is calculated from the elastic
constant of these compounds, which can be calculated
from the equation given below;
A= 2C44 / (C11 - C12) (2)
Material having anisotropy factor A smaller or greater
than 1, indicates anisotropy behavior, while show isotropic
behavior if the value of A is equal to 1 [31]. It is clear from
Table 2, that all the listed compounds show anisotropic
behaviour in the zinc blend (B3) phase.
From the elastic constants Cij we can also calculate
shear modulus (G), Young’s modulus (E), Pugh’s index of
ductility (B/G) and Poisson’s ratio ν, using Voigt–Reus
Hill approximations and the following expressions [33-
36]:
GBBG
E
39
(3)
)34
)(5
121144
121144 CCC CCC
GR
(4)
)3(
5
1
441211 CCCGV
(5)
The shear modulus G is given by:
GGG RV
(6)
The stiffness of materials depends upon the Young’s
modulus (E) of the material, higher the Young’s modulus
(E) stiffer will be the materials. It is clear from Table 2
that CuF with E= 77.30, is much stiffer than the remaining
listed compounds in this table. Important property of the
elastic constant parameters is to calculate the ductility and
brittleness of a material. Different parameters (Cauchy
pressure, Pugh’s index, Poisson’s ratio) are used for
calculating the brittleness and ductility of material. We are
using here the Pugh’s index of ductility for the compounds
CuX (X= F, Cl, Br, I).
The ductility index is calculated by the pugh’s (B/G)
[37] ratio. The critical number of B/G ratio is 1.75 which
separates ductile from the brittle material. Greater the B/G
ratio, high will be the ductility and smaller the B/G ratio,
brittle will be the material [31]. It’s clear from the B/G
ratio in Table 2 that, CuF and CuBr show brittle nature
while CuCl and CuI show ductile behaviour.
Table 2. Calculated elastic constants Cij (in GPa), Young’s modulus E (in GPa), shear modulus G (in GPa), Poisson’s ratio ν,
anisotropy factor A and B/G ratio for CuX (X= F, Cl, Br, I), has been presented along with other theoretical and experimental results.
C11
C12
C44
E
G
Ν
A
B/G
CuF
This work
Theory
Experimental
91.09
-
-
-
8.24
-
-
-
26.09
-
-
-
77.30
-
-
-
31.42
-
-
-
0.23
-
-
-
0.63
-
-
-
1.51
-
-
-
CuCl
This work
Theory
Experimental
58.34
46.47k,
48.57k,48.6
l, 45.28m,
47n, 14.9o
45.4p
73.15
34.82k,
35.87k, 34.8l,
30.91m, 36.2n,
74.1o
36.9p
55.42
13.79k,13.21k,15.3
l, 12.19m, 55.3o
14.9p
10.45
-
-
-
3.56
-
-
-
0.46
-
-
-
-7.48
-
-
-
15.8
-
-
-
CuBr
This work
Theory
Experimental
70.44
64.42k,
53.99k, 44l,
43.5n
-
35.03
50.39k,
40.67k, 32.6l,
34.9n
-
40.16
7.53k, 6.85k, 12.3l
-
72.79
-
-
-
28.92
-
-
-
0.25
-
-
-
2.26
-
-
-
1.73
-
-
-
CuI
This work
Theory
Experimental
39.91
72.39k,50.7
5k, 45.2l,
41.3q,
45.1n,
52.8l,
45.1p
43.09
51.68k,33.80k,
32.2l, 32.1q,
30.7n, 34.4l,
30.7p
45.09
22.72k, 9.50k,
10.4l
-
30.70
-
-
-
11.11
-
-
-
0.38
-
-
-
-28.4
-
-
-
3.90
-
-
-
k[5],l[1],m[38],n[39],o[40],p[41],q[42]
1496 Hamid Ullah, A. H. Reshak, Kalsoom inayat , R.Ali, G. Murtaza, Sheraz, S. A. Khan, H. U. Din, Z. A. Alahmed
3.2 Electronic properties
We have calculated the band structure of the CuX (X=
F, Cl, Br, I) by using EV-GGA and mBJ potentials. It is
clear from Fig. 1 (a), by using EV-GGA potential that the
valence and conduction bands for CuF overlapped with
each other at Fermi level (EF), indicating the metallic
nature of CuF. However when we applied the mBJ
potential, the valence and conduction bands are shifted
away from each other, leading to open a direct energy gap
at Γ-Γ symmetry point. This improvement in the energy
band gap value is attributed to the better predicting ability
of d states of elements by mBJ. The calculated band gap
value of CuF is presented in Table 3. To the best of our
knowledge there is no experimental and theoretical data
available to compare our results for CuF. Thus we have
expected that this work can be used as a reference for
further investigation of physical properties of CuF.
(a)
(b)
Fig. 1(a). Calculated band structure of CuF;
(a) EV-GGA, (b) mBJ.
The calculated electronic band structure of CuCl,
CuBr and CuI using EV-GGA and mBJ potential are
shown in Fig.(2, 3 and 4). These figures clearly show that
the top of the valence band and bottom of the conduction
band are located at Γ-Γ symmetry point, hence CuCl,
CuBr and CuI have direct band gap nature. Hence these
materials are useful for optoelectronic devices
applications. The theoretical results and the experimental
data of the energy band gap of CuCl, CuBr and CuI are
presented in Table 3. This clearly shows that our
calculated values are very close to the experimental data
and much better than the previous theoretical work.
(a)
(b)
Fig. 2. Calculated band structure of CuCl;
(a) EV-GGA, (b) mBJ.
Structural, elastic, optoelectronic and optical properties of CuX (X= F, Cl, Br, I): A DFT study 1497
(a)
(b)
Fig. 3. Calculated band structure of CuBr ;
(a) EV-GGA, (b) mBJ.
(a)
(b)
Fig. 4. Calculated band structure of CuI;
(a) EV-GGA, (b) mBJ.
In the light of these results it is obvious that our
calculated energy band structures using EV-GGA and mBJ
are improved than the previously calculated energy band
gaps by LDA and GGA and very close to the experimental
results. That is attributed to the fact that both of EV-GGA
and mBJ potential are more effective and producing better
band splitting than LDA and GGA [43,44] and hence they
bring the energy band gap closer to the experimental one.
Table 3. Calculated energy band gap values for CuX (X= F, Cl, Br, I) in ZB structure in comparison to the other theoretical
works and available experimental data.
Compounds
Energy band structures (eV)
Present Work
Experimental
Other Calculations
EV-GGA
mBJ
LDA/ GGA
CuF
Metallic
4.4
-
-
CuCl
1.22
3.40
3.40a
0.538f, 0.509g
CuBr
2.7
3.00
3.05b,3.09c
0.445f, 0.418g
CuI
2.00
3.10
3.115d,e
1.118f, 1.077g
a[3], b[2], c[17], d[45], e[12], f[4], g[5]
1498 Hamid Ullah, A. H. Reshak, Kalsoom inayat , R.Ali, G. Murtaza, Sheraz, S. A. Khan, H. U. Din, Z. A. Alahmed
3.2.1 Density of states (DOS)
Band structure can be further explored by the density
of states (DOS). We have calculated the total and partial
densities of states for CuX (X= F ,Cl, Br, I) compounds in
the zinc blende (B3) phase using mBJ potential as shown
in Fig. 5(a,b,c), 6(a,b,c), 7(a,b,c), 8(a,b,c). It is clear from
the plots that the valence band (VB) shifts towards Fermi
level with the change of anion from F to I in CuX. This
band is mainly composed of Cu-d and X-p states near the
Fermi level. Above the Fermi level is composed of
mixture of s,p,d states. From Fig. 5(a,b,c), 6(a,b,c),
7(a,b,c), 8(a,b,c), it is seen that Cu-d and X-p states mainly
contribute in the first band, while in the second band (CB)
the s,d states of CuX are rarely involved.
Fig. 5(a). Calculated total densities of states of CuF.
Fig. 5 (b). Calculated partial densities of states of Cu.
Fig. 5(c). Calculated partial densities of states of F.
Fig. 6 (a). Calculated total densities of states of CuCl.
Fig. 6 (b). Calculated partial densities of states of Cu.
Fig. 6 (c). Calculated partial densities of states of Cl.
Fig. 7 (a). Calculated total densities of states of CuBr.
Fig. 7 (b). Calculated partial densities of states of Cu.
Structural, elastic, optoelectronic and optical properties of CuX (X= F, Cl, Br, I): A DFT study 1499
Fig. 7 (c). Calculated partial densities of states of Br.
Fig. 8 (a). Calculated total densities of states of CuI.
Fig. 8 (b). Calculated partial densities of states of Cu.
Fig. 8 (c). Calculated partial densities of states of I.
3.2.2 Electron charge density
The charge density distribution among the atom
explains the bonding nature of material. The sharing of
charges between cation and anion shows covalent bonding
nature, while the transfer of charge among them shows
ionic bonding nature. The charge density plots of CuX
(X= F ,Cl, Br, I) compounds in (1 1 0 ) plane are given in
Fig. 9a-d. It is clear that F shows covalent nature with Cu.
The remaining compounds CuCl, CuBr and CuI shows
covalent nature among anion-anion and anion-cation
atoms.
It is cleared from the figure that the charge is
uniformly shared among cation Cu anion F. Hence the
bonding in copper halides is more covalent. the Fig. shows
that the Cu and F atom do not share the charges, due to the
greater distance they only disturb the charge density
contour round each other. When we replace F by Cl and Br
then it makes strong covalent bonding with Cu atom. If we
replace F by I atom, a weak covalent bond is making as
compared to Cu-Cl and Cu-Br. However, the charge
sharing among the copper cation is not seen in CuF, while
it is seen in the other three compounds. Which shows the
ionic bonding in CuF while covalent bonding in the other
compounds.
(a) Electron density plot of CuF
(b) Electron density plot of CuCl
(c) Electron density plot of CuBr
(d) Electron density plot of CuI
Fig. 9. Calculated charge density plots of CuX (X= F ,Cl,
Br, I) compounds in (1 1 0 ) plane.
1500 Hamid Ullah, A. H. Reshak, Kalsoom inayat , R.Ali, G. Murtaza, Sheraz, S. A. Khan, H. U. Din, Z. A. Alahmed
3.2.3. Optical properties
The dielectric function of the electron gas which is
strongly depends upon the frequency has an important
effect on the physical properties of solids. It explains the
combined excitations of the Fermi sea; for example the
volume and surface plasmons. The dielectric function of a
crystal depends on the electronic band structure, and it is
investigated by optical spectroscopy which is a powerful
tool to determine the band behaviour of solids. It consists
of two parts i.e. real part and imaginary part [46]
     
21 i
(7)
In momentum representation the dielectric function was
calculated, which requires matrix elements of momentum
p in occupied and unoccupied eigenstates. The imaginary
part of the dielectric function
 
2
may be calculated by
using relation [46].
   
k
dS
kP
nn
k
nn BZ nn

2
2
228
(8)
 
2
depends on the joint density of states (
nn
) , and
nn
P
be the momentum matrix element. The real part
 
1
can be obtained from the imaginary part
 
2
by
Kramers-Kronig equation [46]
   
022 2
12
1
dP
(9)
The refractive index
 
n
can be directly calculated
by the relation:
 
2
1
1
2
1
2
2
2
1)()()(
2
1
)(
n
(10)
 
2/1
1
2
1
2
2
2
1)()()(
2
1
)(
k
(11)
We may presume that
 
k
is very small, when the
medium is a weak absorber, so that
1
n
(12)
and
n
k22
(13)
From the above equation it is clear that the refractive
index is determined by the real part of the dielectric
function, while absorption coefficient by imaginary part of
the dielectric functions.
The frequency dependent reflectivity can be
calculated by using the above optical parameters
 
n
and
 
k
by using the following equation:
22
22
)1( )1(
1
~1
~
)( kn kn
n
n
R
(14)
Also the absorption coefficient can be determined from the
dielectric function [47]:
 
2
1
1
2
1
2
2
2
1)()()(2)(2)(
k
(15)
The absorption coefficient from Beer’s law [35]:
ck
c
k
42
(16)
(16)
Fig. 10a-d, is the imaginary part of the dielectric
function of CuX (X= F, Cl, Br, I) for the given energy
ranges. The edge of the optical absorption in CuX (X= F,
Cl, Br, I) take place at around 3.8 eV, 3.3 eV, 1.8 eV and
2.4 eV, respectively. The edge of the optical absorption
occurs at Γ point of the BZ between the valence and
conduction band, these are the threshold for the direct
optical transition. This point is known as the fundamental
absorption edge. Fig. 10a-d, also shows that CuX (X= F,
Cl, Br, I) have a strong absorption between 3.5 eV to 18
eV and 13 eV for CuF and CuCl, while from 3.0 eV to 11
eV for CuBr and CuI respectively.
Fig. 10a-d, illustrated the real parts of the dielectric
function
 
1
for CuX (X= F, Cl, Br, I). Following this
figure one can see that the dielectric constant at the static
limit
 
0
1
depends upon the band gap of the compounds.
There is an inverse relation between band gap and the
values of the dielectric constant at the static limit
 
0
1
.
This inverse relation can be explained by Peen Model [48]
2
)/(1)0( gp
(17)
The energy band gap Eg can be calculated by the
above equation by using the values of
 
0
1
and plasma
energy
p
. It is clear from Fig. 13, 14, 15, 16, that
 
1
for CuX (X= F, Cl, Br, I), increases with the
increase in energy to reach its maximum at about 9.0 eV,
and 8.0 eV for CuF and CuCl, while for CuBr and CuI it
reaches the maximum at 4.9 eV and 4.6 eV respectively,
then it decreasing to negative value at about 11.50 eV for
CuCl, whereas to about 8.50 eV and 7.50 eV for CuBr
and CuCl respectively.
Structural, elastic, optoelectronic and optical properties of CuX (X= F, Cl, Br, I): A DFT study 1501
(a) Dielectric function of CuF
(b) Dielectric function of CuCl
(c) Dielectric function of CuBr
(d) Dielectric function of CuI
Fig. 10. Calculated dielectric functions of
CuX (X= F ,Cl, Br, I) compounds.
4. Conclusion
Theoretical study of the structural, elastic, electronic
and optical properties of cupper hallides are performed
using FP-LAPW method within GGA, EV-GGA and mBJ
potential. These compounds possess a direct band gaps (Γ-
Γ), therefore these materials are widely used for
optoelectronic devices. In the elastic constants it has been
found that CuF and CuBr show brittle nature while CuCl
and CuI show ductile behaviour. It is concluded that mBJ
is an efficient theoretical technique for the calculation of
the band gaps. The results expect that mBJ will be a
successful tool for the band gaps engineering of IB-VIIA
compounds. In these compounds, the peaks in the optical
plots show the transition of electrons from valence band to
the unoccupied states in the conduction band. From the
analysis of optical spectra, it is predicted that these
materials are useful for optical devices in the infrared,
visible and ultraviolent energy ranges.
Acknowledgement
The result was developed within the CENTEM
project, reg. no. CZ.1.05/2.1.00/03.0088, co-funded by the
ERDF as part of the Ministry of Education, Youth and
Sports OP RDI program. Computational resources were
provided by MetaCentrum (LM2010005) and CERIT-SC
(CZ.1.05/3.2.00/08.0144) infrastructures.
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________________________
*Corresponding author: hamidullah@yahoo.com
hamidullah2k@yahoo.com
... The copper halide based materials (CuCl, CuBr, and CuI) are an interesting class of materials 16,17 because of their direct band gap (3.39 eV for CuCl, 2.91 eV for CuBr, and 2.95 eV for CuI) and optoelectronic applications. 18,19 Interestingly, the band structure of these materials shows similar dispersion though the valence band edge position changes with the nature of the halide. 19,20 However, the conduction band edge position remains more or less the same irrespective of the nature of the halide with respect to the absolute vacuum scale (AVS). ...
... 18,19 Interestingly, the band structure of these materials shows similar dispersion though the valence band edge position changes with the nature of the halide. 19,20 However, the conduction band edge position remains more or less the same irrespective of the nature of the halide with respect to the absolute vacuum scale (AVS). 20,21 Interestingly, among all these Cu based halides and some of the copper oxide based materials (such as Cu 2 O and CuO), CuCl has a more stabilized valence band, which is certainly promising for the water oxidation reaction. ...
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