25,156 research outputs found
Phonons and related properties of extended systems from density-functional perturbation theory
This article reviews the current status of lattice-dynamical calculations in
crystals, using density-functional perturbation theory, with emphasis on the
plane-wave pseudo-potential method. Several specialized topics are treated,
including the implementation for metals, the calculation of the response to
macroscopic electric fields and their relevance to long wave-length vibrations
in polar materials, the response to strain deformations, and higher-order
responses. The success of this methodology is demonstrated with a number of
applications existing in the literature.Comment: 52 pages, 14 figures, submitted to Review of Modern Physic
Linear-response theory and lattice dynamics: a muffin-tin orbital approach
A detailed description of a method for calculating static linear-response
functions in the problem of lattice dynamics is presented. The method is based
on density functional theory and it uses linear muffin-tin orbitals as a basis
for representing first-order corrections to the one-electron wave functions. As
an application we calculate phonon dispersions in Si and NbC and find good
agreement with experiments.Comment: 18 pages, Revtex, 2 ps figures, uuencoded, gzip'ed, tar'ed fil
Some open questions in TDDFT: Clues from Lattice Models and Kadanoff-Baym Dynamics
Two aspects of TDDFT, the linear response approach and the adiabatic local
density approximation, are examined from the perspective of lattice models. To
this end, we review the DFT formulations on the lattice and give a concise
presentation of the time-dependent Kadanoff-Baym equations, used to asses the
limitations of the adiabatic approximation in TDDFT. We present results for the
density response function of the 3D homogeneous Hubbard model, and point out a
drawback of the linear response scheme based on the linearized Sham-Schl\"uter
equation. We then suggest a prescription on how to amend it. Finally, we
analyze the time evolution of the density in a small cubic cluster, and compare
exact, adiabatic-TDDFT and Kadanoff-Baym-Equations densities. Our results show
that non-perturbative (in the interaction) adiabatic potentials can perform
quite well for slow perturbations but that, for faster external fields, memory
effects, as already present in simple many-body approximations, are clearly
required.Comment: 15 pages, submitted to Chemical Physic
Electronic Structure and Magnetic Properties of Solids
We review basic computational techniques for simulations of various magnetic
properties of solids. Several applications to compute magnetic anisotropy
energy, spin wave spectra, magnetic susceptibilities and temperature dependent
magnetisations for a number of real systems are presented for illustrative
purposes.Comment: Review article; To appear in Journal of Computational Crystallograph
SMD-based numerical stochastic perturbation theory
The viability of a variant of numerical stochastic perturbation theory, where
the Langevin equation is replaced by the SMD algorithm, is examined. In
particular, the convergence of the process to a unique stationary state is
rigorously established and the use of higher-order symplectic integration
schemes is shown to be highly profitable in this context. For illustration, the
gradient-flow coupling in finite volume with Schr\"odinger functional boundary
conditions is computed to two-loop (i.e. NNL) order in the SU(3) gauge theory.
The scaling behaviour of the algorithm turns out to be rather favourable in
this case, which allows the computations to be driven close to the continuum
limit.Comment: 35 pages, 4 figures; v2: corrected typos, coincides with published
versio
Ab-initio investigation of phonon dispersion and anomalies in palladium
In recent years, palladium has proven to be a crucial component for devices
ranging from nanotube field effect transistors to advanced hydrogen storage
devices. In this work, I examine the phonon dispersion of fcc Pd using first
principle calculations based on density functional perturbation theory. While
several groups in the past have studied the acoustic properties of palladium,
this is the first study to reproduce the phonon dispersion and associated
anomaly with high accuracy and no adjustable parameters. In particular, I focus
on the Kohn anomaly in the [110] direction.Comment: 19 pages, preprint format, 7 figures, added new figures and
discussio
Time-Dependent Magnons from First Principles
We propose an efficient and non-perturbative scheme to compute magnetic excitations for extended systems employing the framework of time-dependent density functional theory. Within our approach, we drive the system out of equilibrium using an ultrashort magnetic kick perpendicular to the ground-state magnetization of the material. The dynamical properties of the system are obtained by propagating the time-dependent Kohn–Sham equations in real time, and the analysis of the time-dependent magnetization reveals the transverse magnetic excitation spectrum of the magnet. We illustrate the performance of the method by computing the magnetization dynamics, obtained from a real-time propagation, for iron, cobalt, and nickel and compare them to known results obtained using the linear-response formulation of time-dependent density functional theory. Moreover, we point out that our time-dependent approach is not limited to the linear-response regime, and we present the first results for nonlinear magnetic excitations from first principles in iron
First-principles dynamics of electrons and phonons
First-principles calculations combining density functional theory and
many-body perturbation theory can provide microscopic insight into the dynamics
of electrons and phonons in materials. We review this theoretical and
computational framework, focusing on perturbative treatments of scattering,
dynamics and transport of coupled electrons and phonons. We discuss application
of these first-principles calculations to electronics, lighting, spectroscopy
and renewable energy.Comment: 14 pages, 1 figur
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