60
Table 6.1: Grouping of compounds in Figure 6.3 based on the range of geometric
mean of chemical scale factor
Group Range(p
AB)
1 0.00 - 1.45
2 1.45 - 1.75
3 1.75 - 1.95
4 1.95 - 2.10
5 2.10 - 2.30
6 2.30 - 3.10
Table 6.2: Standard enthalpy H of formation of binary compounds in
wurtzite structure having the bandgap in the range of 1.0 - 3.5 eV chosen
to form ternary wurtzite structures for bandgap engineering of binary compounds.
HOQMD shows the enthalpy of formation of the with same stoichiometry
in the minimum energy structure and Hhull represents the enthalpy
above the convex hull calculated from OQMD database. 73 All the
energies are mentioned in eV/atom.
Compound H HOQMD Hhull Compound H HOQMD Hhull
GaN -0.72 -0.59 -0.13 ZnO -1.77 -1.68 -0.09
ScN -2.05 -2.04 -0.01 GeO -1.03 -1.94 0.45
AgF -0.94 -1.21 0.27 SnO -1.18 -1.58 0.40
PbO -0.97 -1.36 0.39 AgI -0.32 -0.38 0.06
LaN -1.50 -1.44 -0.06 YN -1.97 -1.81 -0.16
InP -0.33 -0.37 0.04 GaP -0.59 -0.55 -0.04
AlAs -0.62 -0.49 -0.14 AlP -0.86 -0.76 -0.10
AgCl -0.56 -0.67 0.11 AgBr -0.46 -0.55 0.09
CdTe -0.37 -0.47 -0.10 AlSb -0.32 -0.17 -0.15
CdSe -0.69 -0.64 -0.05 ZnTe -0.56 -0.47 -0.09
ZnSe -0.90 -0.72 -0.18 CdS -0.75 -0.81 0.06
GeS -0.42 -0.42 0.00 AlI -0.27 -0.05 0.27
AlBr -0.58 -0.31 0.34 GeSe -0.33 -0.22 -0.11
SnS -0.48 -0.66 0.18 SnSe -0.44 -0.48 0.04
PbS -0.41 -0.71 0.30 PbSe -0.38 -0.57 0.19
GeTe -0.05 -0.09 0.04 PbTe -0.05 -0.41 0.36
Figure 6.2 shows the ball and stick model of the crystal structures explored
in the present work. Binary compounds crystallizing in NiAs and wurtzite
structures have four atoms in the unit cell with the coordination number of
six and four respectively, whereas the primitive unit cell of the rocksalt and
zincblende structures contains two atoms with a coordination number of six
and four respectively. In the light of recent experiments on the synthesis of
compounds violating chemical/octet rules under extreme conditions we do not
impose any chemical rules to narrow down the search space in our calculations