A. Shaari

Non-local exchange correlation functionals impact on the structural, electronic and optical properties of III–V arsenides

Exchange correlation (XC) energy functionals play a vital role in the efficiency of density functional theory (DFT) calculations, more soundly in the calculation of fundamental electronic energy bandgap. In the present DFT study of III-arsenides, we investigate the implications of XC-energy functional and corresponding potential on the structural, electronic and optical properties of XAs (X = B, Al, Ga, In). Firstly we report and discuss the optimized structural lattice parameters and the band gap calculations performed within different non-local XC functionals as implemented in the DFT-packages: WIEN2k, CASTEP and SIESTA. These packages are representative of the available code in ab initio studies. We employed the LDA, GGA-PBE, GGA-WC and mBJ-LDA using WIEN2k. In CASTEP, we employed the hybrid functional, sX-LDA. Furthermore LDA, GGA-PBE and meta-GGA were employed using SIESTA code. Our results point to GGA-WC as a more appropriate approximation for the calculations of structural parameters. However our electronic bandstructure calculations at the level of mBJ-LDA potential show considerable improvements over the other XC functionals, even the sX-LDA hybrid functional. We report also the optical properties within mBJ potential, which show a nice agreement with the experimental measurements in addition to other theoretical results.

An Improved Study of Electronic Band Structure and Optical Parameters of X-Phosphides (X=B, Al, Ga, In) by Modified Becke—Johnson Potential

We report the electronic band structure and optical parameters of X-Phosphides (X=B, Al, Ga, In) by first-principles technique based on a new approximation known as modified Becke—Johnson (mBJ). This potential is considered more accurate in elaborating excited states properties of insulators and semiconductors as compared to LDA and GGA. The present calculated band gaps values of BP, AlP, GaP, and InP are 1.867 eV, 2.268 eV, 2.090 eV, and 1.377 eV respectively, which are in close agreement to the experimental results. The band gap values trend in this study is as: Eg(mBJ-GGA/LDA) > Eg(GGA) > Eg(LDA). Optical parametric quantities (dielectric constant, refractive index, reflectivity and optical conductivity) which based on the band structure are also presented and discussed. BP, AlP, GaP, and InP have strong absorption in between the energy range 4–9 eV, 4–7 eV, 3–7 eV, and 2–7 eV respectively. Static dielectric constant, static refractive index and coefficient of reflectivity at zero frequency, within mBJ-GGA, are also calculated. BP, AlP, GaP, and InP show significant optical conductivity in the range 5.2–10 eV, 4.3–8 eV, 3.5–7.2 eV, and 3.2–8 eV respectively. The present study endorses that the said compounds can be used in opto-electronic applications, for different energy ranges.

Electronic structure engineering of ZnO with the modified Becke–Johnson exchange versus the classical correlation potential approaches

In this study, we report investigations of structural and electronic properties of ZnO in wurtzite (WZ), rock salt (RS) and zinc-blende (ZB) phases. Calculations have been done with full-potential linearized augmented plane wave plus local orbital method developed within the frame work of Density Functional Theory (DFT). For structural properties investigations, Perdew and Wang proposed local density approximations (LDA) and Perdew et al. proposed generalized gradient approximations (GGA) have been applied. Where for electronic properties in addition to these, Tran–Blaha modified Becke–Johnson (mBJ) potential has been used. Our computed band gap values of ZnO in WZ and ZB phases with mBJ potential are significantly improved compared to those with LDA and GGA; however, in RS phase, energy gap is significantly overestimated compared to experimental measurements. The Zn-d band was found to be more narrower with mBJ potential than that of LDA and GGA. On the other hand, our evaluated crystal field splitting energy values overestimate the experimental values.

First principles investigations of vinazene molecule and molecular crystal: a prospective candidate for organic photovoltaic applications

AbstractEscalating demand for sustainable energy resources, because of the rapid exhaustion of conventional energy resources as well as to maintain the environmental level of carbon dioxide (CO2) to avoid its adverse effect on the climate, has led to the exploitation of photovoltaic technology manifold more than ever. In this regard organic materials have attracted great attention on account of demonstrating their potential to harvest solar energy at an affordable rate for photovoltaic technology. 2-vinyl-4,5-dicyanoimidazole (vinazene) is considered as a suitable material over the fullerenes for photovoltaic applications because of its particular chemical and physical nature. In the present study, DFT approaches are employed to provide an exposition of optoelectronic properties of vinazene molecule and molecular crystal. To gain insight into its properties, different forms of exchange correlation energy functional/potential such as LDA, GGA, BLYP, and BL3YP are used. Calculated electronic structure of vinazene molecule has been displayed via HOMO-LUMO isosurfaces, whereas electronic structure of the vinazene molecular crystal, via electronic band structure, is presented. The calculated electronic and optical properties were analyzed and compared as well. Our results endorse vinazene as a suitable material for organic photovoltaic applications.n Graphical AbstractVinazene molecule and molecular crystalᅟ

Effect of donor strength of extended alkyl auxiliary groups on optoelectronic and charge transport properties of novel naphtha[2,1-b:6,5-b']difuran derivatives: simple yet effective strategy.

AbstractThe present study spotlights the designing of new derivatives of 2,7-bis (4-octylphenyl) naphtho [2,1-b:6,5-b′] difuran (C8-DPNDF) by substituting the alkyl groups (methyl, ethyl, propyl, butyl, pentyl, hexyl, and heptyl groups) at para position. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods are employed to optimize the molecular structures in ground and first excited states, respectively. Several electro-optical properties including hole/electron reorganization energies (λh/λe), electron affinities (EAs), ionization potentials (IPs), molecular electrostatic potentials (MEP), and frontier molecular orbitals (FMOs) have been evaluated. Furthermore their transfer integrals and intrinsic mobilities values have also been calculated. From this study, it is found that hole mobility of octyl containing derivative is raised to 4.69xa0cm2xa0V−1xa0s−1. Moreover with attaching octyl group, hole transfer integral values have also been enhanced in newly designed derivatives. The balanced hole and electron reorganization energies, and improved transfer integrals lead to enhanced mobility in derivatives with octyl group, highlighting them as an efficient hole transfer material. Unlike the other electro-optical properties, the intrinsic hole mobility has increased because of transfer integral values of octyl containing derivative C8-DPNDF due to the dense and close crystal packing of C8-DPNDF. However, photostability of furan-based materials has not changed by increasing length of extended alkyl chain. Thus our present investigation highlights the importance of alkyl auxiliary groups that are often neglected/replaced with simple methyl group to save computation costs.n Graphical AbstractThe hole and electron reorganization energies of naphtho[2,1-b:6,5-b]difuran derivatives

How does the increment of hetero-cyclic conjugated moieties affect electro-optical and charge transport properties of novel naphtha-difuran derivatives? A computational approach

AbstractWe have investigated computationally the effects of π-conjugation extension on naphtha[2,1-b:6,5-b’] difuran (DPNDF); where we increase the number of fused NDF (central core) and furan rings in the parent molecule. The molecular structures of all analogues have been optimized at the ground (S0) and first excited (S1) states using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively. Then highest occupied molecular orbitals (HOMOs), the lowest unoccupied molecular orbitals (LUMOs), photophysical properties, adiabatic/vertical electron affinities (EAa)/(EAv), adiabatic/vertical ionization potentials (IPa)/(IPv), and hole/electron reorganization energies λh/λe have been investigated. The effect of NDF and furan rings on structural and electro-optical properties has also been studied. Our calculated reorganization energies of 1a, 1b, and 2c reveal them, materials with balanced hole/electron charge transport, whereas 2a and 2b are good hole-transport materials. By increasing the number of furan rings; the photostability was augmented in 2a, 2b, and 2c.n Graphical AbstractComputed emission spectra, at the TD-B3LYP/6-31G** level of theory

Structural and electronic properties of ni-doped ZnO in zinc-blende phase: A DFT investigations

In the present work investigations of structural and electronic properties of nickel doped ZnO in zinc-blende phase have been done in the framework of density functional theory. In doping process 25% cations (Zn atoms) have been replaced by Ni atoms. Wu-Cohen parameterized Generalized Gradient Approximation (GGA-WC) is used for exchange and correlation energy functional treatment. Our calculations for structural properties reveal a reduction in lattice constant with Ni doping. Whereas the spin polarized electronic structures show metallic behavior of ZnO in the presence of Ni impurity atoms for both up and down spin configuration. Moreover we present calculated density of states to understand the effect of Ni doping on ZnO.

Thiophene/Graphene Interface Peculiarities for Potential Organic Electronic Applications

Interfacial study between thiophene molecule and graphene surface is presented by employing density functional theory methods. To do so, interfacing separation distance is varied from 1.00A to 2.50A. Our reported HOMO-LUMO energy gap values, adsorption energy as well as binding energy show the existence of intermolecular forces accumulated from the attractive van der Waals and Pauli repulsion forces. It is noted subsequently that the growing intermolecular forces are very sensitive even to relatively a small change in the interfacing separation distance between the molecule and surface. In the electronic density of states, dense electrons population of the thiophene/graphene system is found with appearance of spinpolarization at energy Fermi level. Moreover, a slight magnetic behaviour on thiophene molecule, accompanied by a decrease in the magnetization of graphene surface, is observed in the presence of the molecule near to the surface.

Structure-dependent optoelectronic properties of perylene, di-indenoperylene (DIP) isolated molecule and DIP molecular crystal

Theoretical simulations were designed by first principles approach of density functional theory to investigate the structural and optoelectronic properties of different structural classes of perylene; isolated perylene, diindeno[1,2,3-cd:1′,2′,3′-lm]perylene (DIP) molecule and DIP molecular crystal. The presence of molecular interactions in DIP crystal proved its structure-dependent behaviours. The herringbone molecular arrangement of DIP crystal has influenced the electronic properties by triggering the intermolecular interactions that reduced the energy gaps between HOMO and LUMO of the crystal. Strong hybridization resulting from dense charges population near zero Fermi energy has pushed valence band maxima in the density of states of all perylene structures to higher energies. Under small energy input, charges are transferred continuously as observed in the spectra of conductivity and dielectric. The existence of strong absorption intensities are consistent with the former works and supported by the obtained polarized reflectivity and loss spectra.

Advances in CZTS thin films and nanostructured

Abstract Already published data for the optical band gap (Eg) of thin films and nanostructured copper zinc tin sulphide (CZTS) have been reviewed and combined. The vacuum (physical) and non-vacuum (chemical) processes are focused in the study for band gap comparison. The results are accumulated for thin films and nanostructured in different tables. It is inferred from the re- view that the nanostructured material has plenty of worth by engineering the band gap for capturing the maximum photons from solar spectrum.