Mazmira Mohamad

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. Graphical AbstractVinazene molecule and molecular crystalᅟ

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.

DFT Investigations of the Optical Properties of Gallium Arsenide

Gallium Arsenide (GaAs) because of having unique characteristics like direct band gap, higher electron mobility and saturated electron velocity etcetera, has wide applications specifically in optoelectronic devices. In this research work we present a comprehensive density functional theory (DFT) based first principles study of optical properties of GaAs. Exchange correlation functional (XC) play a key role in the DFT investigations. A comparative study of the optical properties is presented based upon local density approximation (LDA) by Perdew and wang, Perdew-Burke-Ernzerhof parameterized generalized gradient approximation (GGA-PBE), Wu-Cohen parameterized GGA (GGA-WC) and Engel and Vosko proposed GGA (GGA-EV). Computations in this study have been performed by full potential (FP) linearized augmented plane wave (LAPW) plus local orbitals (lo) approach designed within DFT as realized in the computational code WIEN2k. Our investigations, for the optical properties of GaAs with mentioned XC potentials, cover detailed analysis of dielectric functions, absorption coefficient α (ω), energy loss functions, reflectivity R(ω), refractive index n (ω) and extinction coefficient k (ω). The analysis shows that the optical parameters calculated with GGA-PBE are comparatively reasonable and closer to the experimental results. Keywords: Density functional theory, local density approximation, gradient and other corrections, APW calculations, Dielectric function, absorption and reflection spectra PACS: 71.15.Mb, 71.15.Ap, 77.22.Ch, 78.40.Pg