Papers by Keyword: Local Density Approximation

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Authors: N. Najwa Anua, R. Ahmed, A. Shaari, Ul Haq Bakhtiar, Mazmira Binti Mohamad
Abstract: 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
Authors: Bakhtiar Ul Haq, R. Ahmed, A. Shaari, R. Hussain, Mazmira binti Mohamad
Abstract: The injection impurity element into ZnO has added new dimension to its versatile applications particularly in spintronics and optoelectronics. In this work, we are reporting effect of non magnetic Ti, and magnetic V impurities in ZnO. The substitution of impurity atoms have been done in ground state wurtzite (WZ) and meta stable zinc-blende (ZB) structure. Our investigations have revealed a small difference in WZ and ZB geometries of contaminated ZnO reflecting on the possibility of their experimental fabrication. Spin polarized electronic structures resembled nonmagnetic nature of Ti:ZnO in WZ and magnetic nature in ZB geometry. Similarly introduction of V in to ZnO induced magnetization in ZnO in both WZ and ZB geometry. For these investigations, we have adapted DFT approach using FP-L(APW+lo) method implemented in WIEN2k code.
Authors: Ul Haq Bakhtiar, Rashid Ahmed, A. Shaari, Muhammad Zaki bin Yaacob
Abstract: As a transparent conducting oxide, Cd:ZnO system is considered potential candidate for optoelectronic applications alternate to Al:ZnO. However instability issue of the Cd:ZnO system is under debate. Here we investigate effect of Cd impurities on physical properties of ZnO in wurtzite (WZ) as well as zincblende (ZB) geometries. Density functional theory (DFT) based full potential linearized augmented plane wave plus local orbital FP-L(APW+lo) method has been adapted for these investigations. To calculate the total energy of the system, exchange correlation energy term is evaluated at the level of GGA. For the more realistic band gap calculation, GGA in addition to mBJ exchange potential has been employed. From our calculations, it is observed, Cd:ZnO is more stable in ZB structure than that of WZ. The Cd substitution ZnO has a tendency to convert the hexagonal geometry into cubic. It is also observed, doping of the Cd impurities strongly influence the electronic structures resulting into the narrowing energy band gap.
Authors: Satoru Masatsuji, Yoshifumi Noguchi, Soh Ishii, Kaoru Ohno
Authors: P.A. Sterne, J.H. Kaiser, J.C. O'Brien, Richard H. Howell
Authors: F. Plazaola, A.P. Seitsonen, M.J. Puska
Authors: Manjeera Mantina, Long Qing Chen, Zi Kui Liu
Abstract: A simplified approach to predicting diffusion coefficients directly from first-principles is proposed. In this approach, the atomic jump frequencies are calculated through the Eyring’s reaction rate theory while the temperature dependence of diffusion coefficients are accounted using phonon theory within the quasi-harmonic approximation. The procedure can be applied to both self-diffusion and impurity diffusion coefficients and different crystal systems. Applications to self-diffusion coefficients in fcc Cu, bcc Mo, hcp Mg and impurity diffusion coefficients of Li in fcc Al, W in bcc Mo and Cd in hcp Mg show agreement with experimental measurements.
Authors: M.M. De Souza, E.M. Sankara Narayanan
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