Journal of Solid State Chemistry 207 (2013) 140–146
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Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Ab initio density functional theory investigation of the structural,
electronic and optical properties of Ca3Sb2 in hexagonal and
cubic phases
Borhan Arghavani Nia a,n, Matin Sedighi a, Masoud Shahrokhi b, Rostam Moradian c,d
a
Department of Physics, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran
Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran
c
Nano-Science and Nano-Technology Research Center, Razi University, Kermanshah, Iran
d
Computational Physics Science Research Laboratory, Department of Nano-Science, Institute for Studies in Theoretical Physics and Mathematics (IPM),
P.O. Box 19395-1795, Tehran, Iran
b
art ic l e i nf o
a b s t r a c t
Article history:
Received 28 May 2013
Received in revised form
7 September 2013
Accepted 16 September 2013
Available online 25 September 2013
A density functional theory study of structural, electronical and optical properties of Ca3Sb2 compound in
hexagonal and cubic phases is presented. In the exchange–correlation potential, generalized gradient
approximation (PBE-GGA) has been used to calculate lattice parameters, bulk modulus, cohesive energy,
dielectric function and energy loss spectra. The electronic band structure of this compound has been
calculated using the above two approximations as well as another form of PBE-GGA, proposed by Engle
and Vosko (EV-GGA). It is found that the hexagonal phase of Ca3Sb2 has an indirect gap in the Γ-N
direction; while in the cubic phase there is a direct-gap at the Γ point in the PBE-GGA and EV-GGA.
Effects of applying pressure on the band structure of the system studied and optical properties of these
systems were calculated.
& 2013 Elsevier Inc. All rights reserved.
Keywords:
DFT
Ca3Sb2
Semiconductor
Band structure and pressure
1. Introduction
Recently, wide band gap semiconductors have attracted considerable attention due to their great potential applications in
electronic and optoelectronic devices. It is well known that the
combination of the second group with the fifth group elements of
periodic table leads to wide band gap extrinsic semiconductor.
Combinations of the calcium with the fifth group such as Ca3P2
and Ca3N2 have been investigated [1,2]. Phase diagram of calcium
and antimony combination was investigated at different temperatures [3,4]. It is found that calcium and antimony combinations are
formed in the Ca3Sb2, Ca2Sb, Ca5Sb3, Ca11Sb10 and CaSb2 systems.
Ca3Sb2 crystallizes in both body center cubic (bcc) and hexagonal
structures. Ca3Sb2 has the space group of Ia3 (2 0 6) in the body
center cubic phase and the space group of La2O3 (1 6 4) in the
hexagonal phase [5]. Due to the similar structures for the combination of the second group with the fifth group elements such as
Mg3Pn2 (where Pn ¼N, P, As, Sb) and Ca3N2 and Ca3P2 [6–8], it is
expected that Ca3Sb2 in both hexagonal and cubic phases would
have semiconductor properties. So far thermodynamic properties
of Ca3Sb2 such as the Gibbs free energy, enthalpy, heat capacity Cp,
n
Corresponding author. Tel.: þ 98 9183300731.
E-mail address: [email protected] (B. Arghavani Nia).
0022-4596/$ - see front matter & 2013 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jssc.2013.09.026
have been investigated, but there is no report on the structural,
electronical and optical properties of Ca3Sb2 [9]. In this paper we
investigated the structural, electronical and optical properties of
Ca3Sb2 in the hexagonal and cubic phases using density functional
theory calculations. The paper is organized as follows: first the
computational details are presented followed by the results and
discussion, concluding remarks are given in the last section.
2. Computational details
All calculations presented in this work are based on the density
functional theory (DFT) [10,11] using all the electrons, full potential code WIEN2K [12]. For the exchange–correlation energy
functional, we used the generalized gradient approximation
(PBE-GGA) in the form of Perdew et al. (PBE-GGA) [13] and
Engel–Vosko (EV-GGA) [14]. The EV-GGA has been developed for
the calculation of the energy band structure, which is based on the
optimized potential but it is not used in the calculations of
structural parameters. The radii of the muffin-tin spheres (RMT)
were set to as RCa ¼2.6 a.u. and RSb ¼2.8 a.u. in hexagonal phase
and RCa ¼2.4 a.u. and RSb ¼2.7 a.u. in cubic phase. The maximum
angular momentum of the atomic orbital basis functions was set to
lmax ¼ 10. In order to achieve energy eigenvalues convergence, the
wave functional in the interstitial region was expanded in terms of