Investigation of structural, electronic, and optical properties of the
monoclinic and triclinic polymorphs of hexamethylenetetraminium
2,4-dinitrophenolate monohydrate ðC
6
H
13
N
þ
4
$ C
6
H
3
N
2
O
5
$H
2
OÞ
compound: A DFT approach
Zeyad A. Alahmed
a, *
, A.H. Reshak
b, c
, Suchada Chantrapromma
d
, Hoong-Kun Fun
e
a
Department of Physics and Astronomy, College of Science, King Saud University, Riyadh 11451, Saudi Arabia
b
New Technologies-Research Center, University of West Bohemia, Univerzitni 8, Pilsen 30614, Czech Republic
c
Center of Excellence Geopolymer and GreenTechnology, School of Material Engineering, University Malaysia Perlis, Kangar 01007, Perlis, Malaysia
d
Department of Chemistry, Faculty of Science, Prince of Songkla University, Hat-Yai, Songkhla 90112, Thailand
e
Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia
highlights
Electronic and optical properties of two phases of polymorphs were studied by DFT.
The monoclinic polymorph possess an indirect band gap of 1.935 eV using (PBE-GGA).
The triclinic polymorph has an indirect band gap of 1.773 using (PBE-GGA).
The monoclinic and triclinic phases exhibit a wide optical transparency region.
article info
Article history:
Received 25 July 2015
Received in revised form
1 December 2015
Accepted 30 December 2015
Available online xxx
Keywords:
Optical materials
Organic compounds
Electronic materials
Ab initio calculations
Band-structure
abstract
We have investigated the structural, electronic and optical properties for two phases of polymorphs of
hexamethylenetetraminium 2,4-dinitrophenolate monohydrate ðC
6
H
13
N
þ
4
$ C
6
H
3
N
2
O
5
$H
2
OÞ compound
which were synthesized by Hoong-Kun Fun's group. The first phase possesess monoclinic P2
1
/m space
group, while the other phase has triclinic P1 space group. The all electron full potential linearized
augmented plane wave (FP-LAPW þ lo) method within the local density approximation (LDA) and the
Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) were used. Calculation shows
that the conduction band minimum (CBM) for the two phases is located between D and Z points of the
Brillouin zone (BZ) while the valence band maximum (VBM) is located at the center of the BZ, resulting in
an indirect band gap. It has been found that the monoclinic (300 K) polymorph possesses a band gap of
about 1.884 (LDA) and 1.935 (PBE-GGA) eV while triclinic (143 K) polymorph has a band gap of about
1.720 (LDA) and 1.773 (PBE-GGA) eV. For a deeper insight into the electronic structure, we have per-
formed comprehensive optical properties calculations. These confirm the band gap reduction during the
phase transition (300 K/143 K). The bond lengths and angles are calculated and compared with the
experimental data; good agreement was found which reveals the accuracy of the calculations.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
Crystals having different arrangements of the same elements/
compounds in their unit cells are called allotropes/polymorphs
respectively. More precisely, allotropes/polymorphs are crystals
comprising the same elements/compounds but crystallizing out in
different space groups. Allotropes/polymorphs have the same
chemical properties but different physical properties. An excellent
example is given by the different physical properties of the two
allotropes of carbon, namely, graphite and diamond. Polymorphism
can occur with inorganic, organic and biological compounds as well
as in proteins. In pharmacy, polymorphism plays a very crucial role
* Corresponding author.
E-mail address: zalahmed@ksu.edu.sa (Z.A. Alahmed).
Contents lists available at ScienceDirect
Materials Chemistry and Physics
journal homepage: www.elsevier.com/locate/matchemphys
http://dx.doi.org/10.1016/j.matchemphys.2015.12.063
0254-0584/© 2016 Elsevier B.V. All rights reserved.
Materials Chemistry and Physics xxx (2016) 1e10
Please cite this article in press as: Z.A. Alahmed, et al., Investigation of structural, electronic, and optical properties of the monoclinic and triclinic
polymorphs of hexamethylenetetraminium 2,4-dinitrophenolate monohydrate C
6
H
13
N
þ
4
·C
6
H
3
N
2
O
5
·H
2
O compound: A DFT approach,
Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2015.12.063