First-Principles Study of Optical Excitations in Alpha Quartz

1999 ◽  
Vol 579 ◽  
Author(s):  
Eric K. Chang ◽  
Michael Rohlfing ◽  
Steven G. Louie
Keyword(s):  
Absorption Spectrum ◽  
First Principles ◽  
Optical Spectrum ◽  
Quantitative Description ◽  
Frequency Range ◽  
Gw Approximation ◽  
Electron Hole ◽  
Self Energy ◽  
Excitonic Effects

ABSTRACTThe properties of silicon dioxide have been studied extensively over the years. However, there still remain major unanswered questions regarding the nature of the optical spectrum and the role of excitonic effects in this technologically important material. In this work, we present an ab initio study of the optical absorption spectrum of alpha-quartz, using a newly developed first-principles method which includes self-energy and electron-hole interaction effects. The quasiparticle band structure is computed within the GW approximation to obtain a quantitative description of the single-particle excitations. The Bethe-Salpeter equation for the electron-hole excitations is solved to obtain the optical spectrum and to understand the spatial extent and physical properties of the excitons. The theoretical absorption spectrum is found to be in excellent agreement with the measured spectrum. We show that excitonic effects are crucial in the frequency range up to 5 eV above the absorption threshold.

Electronic Structure and Optical Absorption of Fluorographene

2011 ◽  
Vol 1370 ◽  
Author(s):  
Yufeng Liang ◽  
Li Yang
Keyword(s):  
Absorption Spectrum ◽  
Electronic Structure ◽  
Charge Transfer ◽  
Optical Absorption ◽  
Optical Absorption Spectrum ◽  
First Principles ◽  
Gw Approximation ◽  
Exciton Condensation ◽  
Excitonic Effects ◽  
Electron Effects

ABSTRACTA first-principles study on the quasiparticles energy and optical absorption spectrum of fluorographene is presented by employing the GW + Bethe-Salpeter Equation (BSE) method with many-electron effects included. The calculated band gap is increased from 3.0 eV to 7.3 eV by the GW approximation. Moreover, the optical absorption spectrum of fluorographene is dominated by enhanced excitonic effects. The prominent absorption peak is dictated by bright resonant excitons around 9.0 eV that exhibit a strong charge transfer character, shedding light on the exciton condensation and relevant optoelectronic applications. At the same time, the lowest-lying exciton at 3.8 eV with a binding energy of 3.5 eV is identified, which gives rise to explanation of the recent ultraviolet photoluminescence experiment.

Programmable hyperbolic polaritons in van der Waals semiconductors

Science ◽  
2021 ◽  
Vol 371 (6529) ◽  
pp. 617-620 ◽  
Author(s):  
A. J. Sternbach ◽  
S. H. Chae ◽  
S. Latini ◽  
A. A. Rikhter ◽  
Y. Shao ◽  
...  
Keyword(s):  
Transition Metal Dichalcogenide ◽  
Lattice Vibrations ◽  
Frequency Range ◽  
Rydberg Series ◽  
Electron Hole ◽  
Hyperbolic Dispersion ◽  
Quantum Transitions ◽  
Layered Crystals ◽  
Layered Transition Metal

Collective electronic modes or lattice vibrations usually prohibit propagation of electromagnetic radiation through the bulk of common materials over a frequency range associated with these oscillations. However, this textbook tenet does not necessarily apply to layered crystals. Highly anisotropic materials often display nonintuitive optical properties and can permit propagation of subdiffractional waveguide modes, with hyperbolic dispersion, throughout their bulk. Here, we report on the observation of optically induced electronic hyperbolicity in the layered transition metal dichalcogenide tungsten diselenide (WSe2). We used photoexcitation to inject electron-hole pairs in WSe2 and then visualized, by transient nanoimaging, the hyperbolic rays that traveled along conical trajectories inside of the crystal. We establish here the signatures of programmable hyperbolic electrodynamics and assess the role of quantum transitions of excitons within the Rydberg series in the observed polaritonic response.

First Principles Calculation of the Hot Electron Lifetime in Simple and Noble Metals

1999 ◽  
Vol 579 ◽  
Author(s):  
I. Campillo ◽  
A. Rubio ◽  
J. M. Pitarke ◽  
P. M. Echenique
Keyword(s):  
Band Structure ◽  
First Principles ◽  
Free Electron ◽  
Noble Metals ◽  
Electron Gas ◽  
First Principles Calculation ◽  
Hot Electron ◽  
Gw Approximation ◽  
Self Energy ◽  
Low Energy Electrons

ABSTRACTFirst-principles calculations of the inelastic lifetime of low-energy electrons in Al. Cu and Au are reported. Quasiparticle damping rates are evaluated from the knowledge of the electron self-energy, which we compute within the GW approximation. Inelastic lifetimes are then obtained along various directions of the electron wave vector, with full inclusion of the band structure of the solid. Average lifetimes are also reported, as a function of the electron energy. In Al splitting of the band structure over the Fermi level yields electron lifetimes that are smaller than those of electrons in a free-electron gas. In Cu and Au, a major contribution from d electrons participating in the screening of electron-electron interactions yields electron lifetimes which are well above those of electrons in a free-electron gas with the electron density equal to that of valence (4s1 and 6s1 respectively) electrons.

Role of dislocations in the bcc-hcp transition under high pressure: A first-principles approach in beryllium

2020 ◽  
Vol 4 (6) ◽  
Author(s):  
Vanessa Riffet ◽  
Bernard Amadon ◽  
Nicolas Bruzy ◽  
Christophe Denoual
Keyword(s):  
High Pressure ◽  
First Principles

A first-principles study of the atomic layer deposition of ZnO on carboxyl functionalized carbon nanotubes: the role of water molecules

2021 ◽  
Vol 23 (5) ◽  
pp. 3467-3478
Author(s):  
J. I. Paez-Ornelas ◽  
H. N. Fernández-Escamilla ◽  
H. A. Borbón-Nuñez ◽  
H. Tiznado ◽  
Noboru Takeuchi ◽  
...  
Keyword(s):  
First Principles ◽  
Ligand Exchange ◽  
Functional Group ◽  
Atomic Layer ◽  
High Reactivity ◽  
Water Molecules ◽  
Exchange Reactions ◽  
Layer Deposition ◽  
The Right

Atomic description of ALD in systems that combine large surface area and high reactivity is key for selecting the right functional group to enhance the ligand-exchange reactions.

INFLUENCE OF La2O3 ADDITIONS ON CHEMICAL DURABILITY AND DIELECTRIC PROPERTIES OF BOROALUMINOSILICATE GLASSES

2012 ◽  
Vol 19 (06) ◽  
pp. 1250062 ◽  
Author(s):  
X. H. ZHANG ◽  
Y. L. YUE ◽  
H. T. WU
Keyword(s):  
Dielectric Properties ◽  
Chemical Durability ◽  
Tangent Loss ◽  
Frequency Range ◽  
Scanning Calorimetry ◽  
Glass Transition Temperatures ◽  
Weight Losses ◽  
Quenching Method ◽  
Scanning Electron

Boroaluminosilicate glasses containing La2O3 were prepared by the normal quenching method. The glass transition temperatures (Tg) were measured by differential scanning calorimetry (DSC). The structural role of RO was investigated by nuclear magnetic resonance (NMR). Chemical durability was evaluated by weight losses of glass samples after immersion in HC1 solution. High resolution scanning electron microscopy (HR-SEM) was used to examine the surface micrographs of corroded glass samples. The dielectric constant and tangent loss were measured in the frequency range 10–106 Hz. The results revealed that chemical durability and dielectric properties increased with increasing La2O3 content.

Sign in / Sign up

Export Citation Format

Share Document