The Urbach tail in silica glass from first principles

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We present density-functional theory calculations of the optical absorption spectra of silica glass for temperatures up to 2400K. The calculated spectra exhibit exponential tails near the fundamental absorption edge that follow the Urbach rule, in quantitative agreement with experiments. We discuss the accuracy of our results by comparing to hybrid exchange correlation functionals. We derive a simple relationship between the exponential tails of the absorption coefficient and the electronic density-of-states, and thereby establish a direct link between the photoemission and the absorption spectra near the absorption edge. We use this relationship to determine the lower bound to the Urbach frequency ... continued below

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7 p. (0.1 MB)

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Sadigh, B; Erhart, P; Aberg, D; Trave, A; Schwegler, E & Bude, J June 15, 2010.

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We present density-functional theory calculations of the optical absorption spectra of silica glass for temperatures up to 2400K. The calculated spectra exhibit exponential tails near the fundamental absorption edge that follow the Urbach rule, in quantitative agreement with experiments. We discuss the accuracy of our results by comparing to hybrid exchange correlation functionals. We derive a simple relationship between the exponential tails of the absorption coefficient and the electronic density-of-states, and thereby establish a direct link between the photoemission and the absorption spectra near the absorption edge. We use this relationship to determine the lower bound to the Urbach frequency regime. We show that in this frequency interval, the optical absorption is Poisson distributed with very large statistical fluctuations. We determine the upper bound to the Urbach frequency regime by identifying the frequency at which transition to Poisson distribution takes place.

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7 p. (0.1 MB)

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PDF-file: 7 pages; size: 0.1 Mbytes

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  • Journal Name: Physical Review Letters; Journal Volume: 106; Journal Issue: 2

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  • Report No.: LLNL-JRNL-436813
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 1030195
  • Archival Resource Key: ark:/67531/metadc832175

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  • June 15, 2010

Added to The UNT Digital Library

  • May 19, 2016, 3:16 p.m.

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  • April 17, 2017, 12:45 p.m.

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Sadigh, B; Erhart, P; Aberg, D; Trave, A; Schwegler, E & Bude, J. The Urbach tail in silica glass from first principles, article, June 15, 2010; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc832175/: accessed September 21, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.