The Urbach tail in silica glass from first principles

Journal Article · Tue Jun 15 00:00:00 EDT 2010 · Physical Review Letters

OSTI ID:1030195

Sadigh, B; Erhart, P; Aberg, D; Trave, A; Schwegler, E; Bude, J

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.

• Research Organization: Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 1030195
• Report Number(s): LLNL-JRNL-436813; PRLTAO; TRN: US201124%%3
• Journal Information: Physical Review Letters, Vol. 106, Issue 2; ISSN 0031-9007
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
42 ENGINEERING
ABSORPTION
ABSORPTION SPECTRA
ACCURACY
DISTRIBUTION
FLUCTUATIONS
FUNCTIONALS
DENSITY FUNCTIONAL METHOD
GLASS
PHOTOEMISSION
SILICA
SPECTRA
TEMPERATURE RANGE 1000-4000 K