scholarly journals Maximally localized Wannier functions for entangled energy bands

2001 ◽  
Vol 65 (3) ◽  
Author(s):  
Ivo Souza ◽  
Nicola Marzari ◽  
David Vanderbilt
Keyword(s):  
Energy Bands ◽  
Wannier Functions

scholarly journals Maximally localized generalized Wannier functions for composite energy bands

1997 ◽  
Vol 56 (20) ◽  
pp. 12847-12865 ◽  
Author(s):  
Nicola Marzari ◽  
David Vanderbilt
Keyword(s):  
Energy Bands ◽  
Wannier Functions ◽  
Composite Energy

scholarly journals Constraining Forces Stabilizing Superconductivity in Bismuth

2017 ◽  
Author(s):  
Ekkehard Krüger
Keyword(s):  
Cooper Pair ◽  
Pair Formation ◽  
Electron Interaction ◽  
Quantum Mechanical ◽  
Cooper Pairs ◽  
Strongly Correlated ◽  
Energy Bands ◽  
Wannier Functions ◽  
Nonadiabatic Heisenberg Model ◽  
Theory Of Superconductivity

As shown in former papers, the nonadiabatic Heisenberg model presents a novel mechanism of Cooper pair formation generated by the strongly correlated atomic-like motion of the electrons in narrow, roughly half-filled "superconducting bands". These are energy bands represented by optimally localized spin-dependent Wannier functions adapted to the symmetry of the material under consideration. The formation of Cooper pairs is not the result of an attractive electron-electron interaction but can be described in terms of quantum mechanical constraining forces constraining the electrons to form Cooper pairs. There is theoretical and experimental evidence that only this nonadiabatic mechanism operating in superconducting bands may produce eigenstates in which the electrons form Cooper pairs. These constraining forces stabilize the Cooper pairs in any superconductor, whether conventional or unconventional. Here we report evidence that also the experimentally found superconducting state in bismuth at ambient as well as at high pressure is connected with a narrow, roughly half-filled superconducting band in the respective band structure. This observation corroborates once more the significance of constraining forces in the theory of superconductivity.

Energy bands and Wannier functions of the fractional Kronig-Penney model

2020 ◽  
Vol 380 ◽  
pp. 125266
Author(s):  
Arianne Vellasco-Gomes ◽  
Rubens de Figueiredo Camargo ◽  
Alexys Bruno-Alfonso
Keyword(s):  
Energy Bands ◽  
Wannier Functions

scholarly journals Wannier functions and ℤ2 invariants in time-reversal symmetric topological insulators

2017 ◽  
Vol 29 (02) ◽  
pp. 1730001 ◽  
Author(s):  
Horia D. Cornean ◽  
Domenico Monaco ◽  
Stefan Teufel
Keyword(s):  
Time Reversal ◽  
Topological Insulators ◽  
Constructive Proof ◽  
Topological Phases ◽  
Energy Bands ◽  
Wannier Functions ◽  
Model Independent ◽  
Dimension 2 ◽  
Topological Obstruction ◽  
Geometric Formula

We provide a constructive proof of exponentially localized Wannier functions and related Bloch frames in 1- and 2-dimensional time-reversal symmetric (TRS) topological insulators. The construction is formulated in terms of periodic TRS families of projectors (corresponding, in applications, to the eigenprojectors on an arbitrary number of relevant energy bands), and is thus model-independent. The possibility to enforce also a TRS constraint on the frame is investigated. This leads to a topological obstruction in dimension 2, related to [Formula: see text] topological phases. We review several proposals for [Formula: see text] indices that distinguish these topological phases, including the ones by Fu–Kane [16], Prodan [33], Graf–Porta [24] and Fiorenza–Monaco–Panati [27]. We show that all these formulations are equivalent. In particular, this allows to prove a geometric formula for the [Formula: see text] invariant of 2-dimensional TRS topological insulators, originally indicated in [16], which expresses it in terms of the Berry connection and the Berry curvature.

Preparation, Electronic Structure and Optical Properties of the Electrochromic Thin Films

2004 ◽  
Vol 9 (4) ◽  
pp. 363-372 ◽  
Author(s):  
T. Lukaszewicz ◽  
A. Ravinski ◽  
I. Makoed
Keyword(s):  
Electrochromic Device ◽  
Orbital Method ◽  
Optical Parameters ◽  
Full Potential ◽  
Electrochromic Devices ◽  
Energy Bands ◽  
Conducting Film ◽  
Recombination Probability ◽  
Transparent Conducting ◽  
Smoluchowski Equations

A new multilayer electrochromic device has been constructed according to the following pattern: glass1/ITO/WO3/gel electrolyte/BP/ITO/glass2, where ITO is a transparent conducting film made of indium and tin oxide and with the surface resistance equal 8–10 Ω/cm2 . The electrochromic devices obtained in the research are characterized by great (considerable) transmittance variation between coloration and bleaching state (25–40% at applied voltage of 1.5 to 3 V), and also high coloration efficiency (above 100 cm2 /C). Selfconsistent energy bands, dielectric permittivity and optical parameters are calculated using a full-potential linear muffin-tin orbital method. The numerical solution of the Debye-Smoluchowski equations is developed for simulating recombination probability of Li+ ions in amorphous electrolyte.

Acoustical Properties of Speech as Indicators of Depression and Suicidal Risk

2008 ◽  
Vol 4 ◽  
Author(s):  
Michael Joshua Landau
Keyword(s):  
Multiple Regression ◽  
Energy Band ◽  
Mental States ◽  
Cross Product ◽  
Female Group ◽  
Suicidal Risk ◽  
Energy Bands ◽  
Band Ratio ◽  
Acoustical Properties ◽  
Male Group

Acoustical properties of speech have been shown to be related to mental states such as remission and depression. The objective of this project was to relate the energy in frequency bands with the severity of the mental state using the Beck Depression Inventory (BDI). Recorded speech was obtained from male and female subjects with mental states of remission, depression, and suicidal risk. These subjects had recorded automated and spontaneous speech samples. Multiple regression analysis was used to relate the independent energy band ratio variables with the dependent BDI scores, and thus allow the determination of equitable BDI scores for future patients. For the male group, the square of the 3rd energy band and the cross-product of the 2nd and 3rd energy band were prominent in both the reading and interviewed groups. Therefore the equation with the 2nd lowest Akaike Information Criterion (AIC) score was chosen for the reading male group, and the 1st lowest AIC score was chosen for the interviewed male group. For the female group, the square and cross-product of the 1st and 2nd energy bands were prominent in both the reading and interviewed groups. Therefore the 2nd lowest AIC score was chosen for the reading female group, and the 1st lowest AIC score was chosen for the interviewed female group. The clinician could thus determine the patient’s mood or state of mind by comparing the estimated BDI score with the ranges of total BDI scores: remitted 0 – 20, depressed 15 – 38, suicidal 38 – 46. Keywords: speech, mental states, power spectra, multiple regression, information theoretic criterion

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