67 research outputs found
Book Reviews
We develop a first-principles approach based on many-body perturbation theory to investigate the effects of the interaction between electrons and carrier plasmons on the electronic properties of highly doped semiconductors and oxides. Through the evaluation of the electron self-energy, we account simultaneously for electron-plasmon and electron-phonon coupling in theoretical calculations of angle-resolved photoemission spectra, electron linewidths, and relaxation times. We apply this methodology to electron-doped anatase TiO2 as an illustrative example. The simulated spectra indicate that electron-plasmon coupling in TiO2 underpins the formation of satellites at energies comparable to those of polaronic spectral features. At variance with phonons, however, the energy of plasmons and their spectral fingerprints depends strongly on the carrier concentration, revealing a complex interplay between plasmon and phonon satellites. The electron-plasmon interaction accounts for approximately 40% of the total electron-boson interaction strength, and it is key to improve the agreement with measured quasiparticle spectra
Temperature dependence of the electronic structure of semiconductors and insulators
The renormalization of electronic eigenenergies due to electron-phonon
coupling is sizable in many materials with light atoms. This effect, often
neglected in ab-initio calculations, can be computed using the
perturbation-based Allen-Heine-Cardona theory in the adiabatic or non-adiabatic
harmonic approximation. After a short description of the numerous recent
progresses in this field, and a brief overview of the theory, we focus on the
issue of phonon wavevector sampling convergence, until now poorly understood.
Indeed, the renormalization is obtained numerically through a q-point sampling
inside the BZ. For q-points close to G, we show that a divergence due to
non-zero Born effective charge appears in the electron-phonon matrix elements,
leading to a divergence of the integral over the BZ for band extrema. Although
it should vanish for non-polar materials, unphysical residual Born effective
charges are usually present in ab-initio calculations. Here, we propose a
solution that improves the coupled q-point convergence dramatically. For polar
materials, the problem is more severe: the divergence of the integral does not
disappear in the adiabatic harmonic approximation, but only in the
non-adiabatic harmonic approximation. In all cases, we study in detail the
convergence behavior of the renormalization as the q-point sampling goes to
infinity and the imaginary broadening parameter goes to zero. This allows
extrapolation, thus enabling a systematic way to converge the renormalization
for both polar and non-polar materials. Finally, the adiabatic and
non-adiabatic theory, with corrections for the divergence problem, are applied
to the study of five semiconductors and insulators: a-AlN, b-AlN, BN, diamond
and silicon. For these five materials, we present the zero-point
renormalization, temperature dependence, phonon-induced lifetime broadening and
the renormalized electronic bandstructure.Comment: 27 pages and 26 figure
Many-body calculations of plasmon and phonon satellites in angle-resolved photoelectron spectra using the cumulant expansion approach
The interaction of electrons with crystal lattice vibrations (phonons) and
collective charge-density fluctuations (plasmons) influences profoundly the
spectral properties of solids revealed by photoemission spectroscopy
experiments. Photoemission satellites, for instance, are a prototypical example
of quantum emergent behavior that may result from the strong coupling of
electronic states to plasmons and phonons. The existence of these spectral
features has been verified over energy scales spanning several orders of
magnitude (from 50 meV to 15-20 eV) and for a broad class of compounds such as
simple metals, semiconductors, and highly-doped oxides. During the past few
years the cumulant expansion approach, alongside with the GW approximation and
the theory of electron-phonon and electron-plasmon coupling in solids, has
evolved into a predictive and quantitatively accurate approach for the
description of the spectral signatures of electron-boson coupling entirely from
first principles, and it has thus become the state-of-the-art theoretical tool
for the description of these phenomena. In this chapter we introduce the
fundamental concepts needed to interpret plasmon and phonon satellites in
photoelectron spectra, and we review recent progress on first-principles
calculations of these features using the cumulant expansion method
Wannier90 as a community code: new features and applications
Wannier90 is an open-source computer program for calculating maximally-localised Wannier functions (MLWFs) from a set of Bloch states. It is interfaced to many widely used electronic-structure codes thanks to its independence from the basis sets representing these Bloch states. In the past few years the development of Wannier90 has transitioned to a community-driven model; this has resulted in a number of new developments that have been recently released in Wannier90 v3.0. In this article we describe these new functionalities, that include the implementation of new features for wannierisation and disentanglement (symmetry-adapted Wannier functions, selectively-localised Wannier functions, selected columns of the density matrix) and the ability to calculate new properties (shift currents and Berry-curvature dipole, and a new interface to many-body perturbation theory); performance improvements, including parallelisation of the core code; enhancements in functionality (support for spinor-valued Wannier functions, more accurate methods to interpolate quantities in the Brillouin zone); improved usability (improved plotting routines, integration with high-throughput automation frameworks), as well as the implementation of modern software engineering practices (unit testing, continuous integration, and automatic source-code documentation). These new features, capabilities, and code development model aim to further sustain and expand the community uptake and range of applicability, that nowadays spans complex and accurate dielectric, electronic, magnetic, optical, topological and transport properties of materials.The WDG acknowledges financial support from the NCCR MARVEL of the Swiss National Science Foundation, the European Union’s Centre of Excellence E-CAM (Grant No. 676531), and the Thomas Young Centre for Theory and Simulation of Materials (Grant No. TYC-101).Peer reviewe
Polymeric nanocapsules prevent oxidation of core-loaded molecules: evidence based on the effects of docosahexaenoic acid and neuroprostane on breast cancer cells proliferation
Advanced capabilities for materials modelling with Quantum ESPRESSO
Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudo-potential and projector-augmented-wave approaches. Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement theirs ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software
Dimensional crossover in the carrier mobility of two-dimensional semiconductors: the case of InSe
Two-dimensional (2D) semiconductors are at the center of an intense research effort aimed at developing the next generation of flexible, transparent, and energy-efficient electronics. In these applications, the carrier mobility, that is the ability of electrons and holes to move rapidly in response to an external voltage, is a critical design parameter. Here, we show that the interlayer coupling between electronic wave functions in 2D semiconductors can be used to drastically alter carrier mobility and dynamics. We demonstrate this concept by performing state-of-the-art ab initio calculations for InSe, a prototypical 2D semiconductor that is attracting considerable attention, because of its exceptionally high electron mobility. We show that the electron mobility of InSe can be increased from 100 cm2 V-1 s-1 to 1000 cm2 V-1 s-1 by exploiting the dimensional crossover of the electronic density of states from two dimensions to three dimensions. By generalizing our results to the broader class of layered materials, we discover that dimensionality plays a universal role in the transport properties of 2D semiconductors
EPW: Electron–phonon coupling, transport and superconducting properties using maximally localized Wannier functions
This program has been imported from the CPC Program Library held at Queen's University Belfast (1969-2018)
Abstract
The EPW (Electron-Phonon coupling using Wannier functions) software is a Fortran90 code that uses density-functional perturbation theory and maximally localized Wannier functions for computing electron–phonon couplings and related properties in solids accurately and efficiently. The EPW v4 program can be used to compute electron and phonon self-energies, linewidths, electron–phonon scattering rates, electron–phonon coupling strengths, transport spectral functions, electronic velocities, resis...
Title of program: EPW
Catalogue Id: AEHA_v2_0
Nature of problem
Calculation of electron and phonon self-energies, linewidths, electron-phonon scattering rates, electron-phonon coupling strengths, transport spectral functions, electronic velocities, resistivity, anisotropic superconducting gaps and spectral functions within the Migdal-Eliashberg theory.
Versions of this program held in the CPC repository in Mendeley Data
AEHA_v1_0; EPW; 10.1016/j.cpc.2010.08.027
AEHA_v2_0; EPW; 10.1016/j.cpc.2016.07.02
Origin of low carrier mobilities in halide perovskites
Halide perovskites constitute a new class of semiconductors that hold promise for low-cost solar cells and optoelectronics. One key property of these materials is the electron mobility, which determines the average electron speed due to a driving electric field. Here we elucidate the atomic-scale mechanisms and theoretical limits of carrier mobilities in halide perovskites by performing a comparative analysis of the archetypal compound CH 3 NH 3 PbI 3 , its inorganic counterpart CsPbI 3 , and a classic semiconductor for light-emitting diodes, wurtzite GaN, using cutting-edge many-body ab initio calculations. We demonstrate that low-energy longitudinal-optical phonons associated with fluctuations of the Pb-I bonds ultimately limit the mobility to 80 cm 2 /(V s) at room temperature. By extending our analysis to a broad class of compounds, we identify a universal scaling law for the carrier mobility in halide perovskites, and we establish the design principles to realize high-mobility materials
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