Physics

In this article we explore the effects of dangling bonds and diameter on the electronic properties of the
wurtzite InAs nanowires (NWs) using the density functional theory. The NWs are confined in the
hexagonal supercell and are simulated in the [0001] direction. The calculations have been carried out by
applying the periodic boundary conditions along the NW axis, i.e., z-Cartesian coordinate, providing
enough vacuum to isolate the system from its neighbors. The optical properties of a material are directly
related to the band-gap; therefore a relationship between the band-gap and diameter of the nanowires
is obtained by using two models, where the band-gap for a larger diameter NW can be estimated. The
results of these models are compared with each other and the effects of the dangling bonds on the
band-gaps are also investigated. The band-gap of the nanowires decreases and the dangling bond ratio
increases with the increase in the diameter of the nanowire, and hence we expect that for large
diameter nanowires the band-gap will approach the band gap of the bulk material. An interesting feature
of the shift in the band-gap from indirect to direct, i.e. optically inactive to active, is also observed in
these NWs with the increase in the diameter.

First principle studies of the cubic rare-earth intermetallics RIn3 and RSn3 (R ¼ La, Ce, Pr, Nd) have been
carried out within the framework of density functional theory using the full potential linearized
augmented plane waves plus local orbital method (FP-LAPW + lo). The calculated structural parameters
with different functionals are found to be consistent with the experimental results. The effect of the
Hubbard potential on the density of states is discussed in detail. It is observed that the inclusion of spin–
orbit coupling (SOC) causes degeneracies of the electronic band structures in the vicinity of the Fermi
level of these compounds. Furthermore, the SOC effect enhances as one goes from La to Nd in a
compound, which demonstrates the interesting nature of this effect in the periodic table. The elastic
constants, bulk moduli, shear moduli, Young’s moduli, anisotropy, Kleinman parameters, Poisson’s ratios,
sound velocities for shear and longitudinal waves, and Debye temperatures are calculated and discussed,
which reveal that these compounds are ductile in nature.

In this paper, we explore the electric field gradients (EFGs) at 238U sites for antiferromagnetic UX2 (X ¼ P, As,
Sb, Bi) using LDA, LDA + U, GGA, GGA + U, and the exact exchange for correlated electrons schemes by
considering the diagonalization of the spin–orbit coupling Hamiltonian in the space of the scalar
relativistic eigenstates using the second-order variational procedure. The electronic structures and
magnetic properties of the compounds are also investigated. It is found that the density functional
theory approaches except exact exchange for correlated electrons are not successful in reproducing the
experimental zero electric field gradient value in UBi2, even LDA + U and GGA + U within their default 4f
density matrices by varying the U parameter in an energy interval of [0; 4 eV], though these techniques
with no need to manually adopt their initial conditions (elements of the occupation matrix) are effective
in the calculation of the nonzero electric field gradients for the other compounds. The exact exchange
for correlated electrons has efficiently provided a null electric field gradient in UBi2 and nonzero electric
field gradients for the other compounds by adjusting its dimensionless parameter a to 0.4. The physics
of the null electric field gradient in UBi2 is revealed in this article and it is discussed that the source of the
ignorable electric field gradient originates from the antiferromagnetic ordering of [Y as compared to the
long-range antiferromagnetic ordering of [[YY in the other compounds. Furthermore, our calculated
magnetic moments for the uranium atoms in these compounds are consistent with the available
experimentally measured values as compared to the severely underestimated theoretical results.

In this paper, the structural, elastic, and electronic properties of RIn3 and RSn3 (R ¼ Sm, Eu, Gd)
compounds have been investigated using the full potential linearized augmented plane wave plus
local orbital method within the density functional theory. The structural properties are investigated
using the LDA, GGA, and the band correlated LDAþU and GGAþU schemes. The lattice
parameters are in good agreement with the available experimental results and the divalent state of
Eu is also verified. The spin-orbit coupling is included in order to predict the correct electronic
properties and splitting of 4f states of the rare earth elements is also incorporated. We calculated
Bulk modulus, shear modulus, Young’s modulus, anisotropic ratio, Kleinman parameters,
Poisson’s ratio, Lame’s co-efficient, sound velocities for shear and longitudinal waves, and Debye
temperature. We also predict the Cauchy pressure and B/G ratio in order to explore the ductile and
brittle behaviors of these compounds.