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First-principles investigation of the optical properties of gold and its alloys

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  1. Tez No: 508557
  2. Yazar: DENİZ KEÇİK
  3. Danışmanlar: Dr. Helena Van Swygenhoven
  4. Tez Türü: Doktora
  5. Konular: Metalurji Mühendisliği, Metallurgical Engineering
  6. Anahtar Kelimeler: First-principles, Density Functional Theory, Many-body Perturbation Theory, Optical Properties, Gold, Gold-alloys, Color
  7. Yıl: 2013
  8. Dil: İngilizce
  9. Üniversite: Ecole Polytechnique Fédérale de Lausanne (EPFL)
  10. Enstitü: Yurtdışı Enstitü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 157

Özet

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Özet (Çeviri)

The electronic and optical properties of metals can be computed from first-principles approaches. Such electronic structure calculations serve as an outstanding tool for the prediction of optical properties and color of precious metals, especially when experimental work is exhaustive and expensive. Gold-based alloys have always been attractive targets for the discovery of their novel colors. We focus in this thesis on modeling the optical spectra of gold and gold-based alloys. For the first part, a comparative approach is employed in terms of the ab-initio techniques utilized. The performances of advanced first-principles methods are evaluated for computation of the optical properties of bulk gold, linking them with the electronic bandstructure. The methods considered are the Density Functional Theory (DFT) and Many-Body Perturbation Theory (MBPT). Within the DFT framework, various exchange-correlation functionals are taken into account: Local Density Approximation (LDA), Generalized Gradient Approximation (GGA) within the Perdew-Burke-Ernzerhof (PBE) formalism and Hybrid functional (HSE06). For the many-body scheme, the nonself consistent GW (G0W0) and quasiparticle self-consistent GW (QSGW) approaches are adopted. For all the methods, the complex dielectric function and the frequency dependent reflectivity are calculated. Moreover, the optical spectra are interpreted by relating them with the bandstructure of bulk Au. It has been found that the local and semi-local XC functionals led to the well-known underestimation of the band gap, along with a redshift of the optical spectra. In contrast, the HSE hybrid functional opened up by too much the interband gap of Au, as well shifting the spectra towards the blue. Furthermore, the G0W0 scheme provided bandstructure and spectra similar as the LDA and GGA approaches. The quasiparticle corrections to the Kohn-Sham eigenvalues in the QSGW approach revealed however results in better agreement with the experiments. In the second part of the thesis, the optical properties of gold-based alloys are computed. The well-known AuAl2 intermetallic compound is taken as a reference system. Mostly standard-DFT, and partially HSE are employed as first-principles approaches. The trends in the optical properties are investigated, when doping subtitutionally the Au in AuAl2 with Pt, at increments of 25 at.%. A systematical shift was observed in the interband absorption edge and reflectivity, when going from one stoichiometry to another. The colors predicted from all the systems are quantitatively presented.

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