Search results for "Density Functional Theory."
showing 10 items of 935 documents
Density-Functional Theory of Quantum Freezing: Sensitivity to Liquid-State Structure and Statistics
1997
Density-functional theory is applied to compute the ground-state energies of quantum hard-sphere solids. The modified weighted-density approximation is used to map both the Bose and the Fermi solid onto a corresponding uniform Bose liquid, assuming negligible exchange for the Fermi solid. The required liquid-state input data are obtained from a paired phonon analysis and the Feynman approximation, connecting the static structure factor and the linear response function. The Fermi liquid is treated by the Wu-Feenberg cluster expansion, which approximately accounts for the effects of antisymmetry. Liquid-solid transitions for both systems are obtained with no adjustment of input data. Limited …
Correlation effects in bistability at the nanoscale: Steady state and beyond
2012
The possibility of finding multistability in the density and current of an interacting nanoscale junction coupled to semi-infinite leads is studied at various levels of approximation. The system is driven out of equilibrium by an external bias and the nonequilibrium properties are determined by real-time propagation using both time-dependent density functional theory (TDDFT) and many-body perturbation theory (MBPT). In TDDFT the exchange-correlation effects are described within a recently proposed adiabatic local density approximation (ALDA). In MBPT the electron-electron interaction is incorporated in a many-body self-energy which is then approximated at the Hartree-Fock (HF), second-Born,…
Density Functional Theory of Multicomponent Quantum Dots
2004
Quantum dots with conduction electrons or holes originating from several bands are considered. We assume the particles are confined in a harmonic potential and assume the electrons (or holes) belonging to different bands to be different types of fermions with isotropic effective masses. The density functional method with the local density approximation is used. The increased number of internal (Kohn-Sham) states leads to a generalisation of Hund's first rule at high densities. At low densitites the formation of Wigner molecules is favored by the increased internal freedom.
Correlation energy of two-dimensional systems: Toward non-empirical and universal modeling
2009
The capability of density-functional theory to deal with the ground-state of strongly correlated low-dimensional systems, such as semiconductor quantum dots, depends on the accuracy of functionals developed for the exchange and correlation energies. Here we extend a successful approximation for the correlation energy of the three dimensional inhomogeneous electron gas, originally introduced by Becke [J. Chem. Phys. {\bf 88}, 1053 (1988)], to the two-dimensional case. The approach aims to non-empirical modeling of the correlation-hole functions satisfying a set of exact properties. Furthermore, the electron current and spin are explicitly taken into account. As a result, good performance is …
Density gradients for the exchange energy of electrons in two dimensions
2009
We derive a generalized gradient approximation to the exchange energy to be used in density functional theory calculations of two-dimensional systems. This class of approximations has a long and successful history, but it has not yet been fully investigated for electrons in two dimensions. We follow the approach originally proposed by Becke for three-dimensional systems [Int. J. Quantum Chem. 23, 1915 (1983), J. Chem. Phys. 85, 7184 (1986)]. The resulting functional depends on two parameters that are adjusted to a test set of parabolically confined quantum dots. Our exchange functional is then tested on a variety of systems with promising results, reducing the error in the exchange energy b…
Analytic density functionals with initial-state dependence and memory
2013
We analytically construct the wave function that, for a given initial state, produces a prescribed density for a quantum ring with two non-interacting particles in a singlet state. In this case the initial state is completely determined by the initial density, the initial time-derivative of the density and a single integer that characterizes the (angular) momentum of the system. We then give an exact analytic expression for the exchange-correlation potential that relates two non-interacting systems with different initial states. This is used to demonstrate how the Kohn-Sham procedure predicts the density of a reference system without the need of solving the reference system's Schr\"odinger …
Elementary excitations in superfluidH3e-H4emixtures
2010
We have studied the dynamic structure function of superfluid $^{3}\text{H}\text{e-}^{4}\text{H}\text{e}$ mixtures at zero temperature as a function of pressure and $^{3}\text{H}\text{e}$ concentration. Results obtained in the full random-phase approximation (RPA) plus density-functional theory and in a generalized Landau-Pomeranchuk approach are presented and compared with experiment. Analytic expressions for several sum rules of the dynamic structure functions have been determined, and have been used to obtain average energies of the collective excitations. In the RPA approach, the dispersion relation of the collective modes shows typical features of level repulsion between zero-soundlike …
Analysis of the plasmonic excitations in assemblies of three-dimensional electron clusters
2020
In the quest to built novel metamaterials with unique optical properties, three-dimensional assemblies of metal clusters and nanoparticles are gathering significant attention. Organized geometries, such as tetrahedra and icosahedra, can be built, for example, by using DNA strands or virus capsids as templates. Here we use the jellium model and time-dependent density functional theory to study the plasmonic resonances in different arrangements of eight-electron clusters from the electronic perspective. A charge transfer ratio index based on the induced transition densities is used to quantify the charge transfer nature of the excitations at different energies. We vary the size, shape, and in…
Photoelectron spectra from first principles: from the many-body to the single-particle picture
2008
We derive a many-body method to evaluate photoelectron spectra of atoms, molecules and clusters from first principles. The excitation energies and the spectroscopic factors are calculated from the linear-response time-dependent density functional theory. The method is applied to noble metal anions, anionic clusters and to neutral small molecules. Our approach shows significant improvement over a simple single-particle treatment and gives an insight into the necessary conditions under which the single-particle picture holds. The consideration of the spectroscopic factor is shown to be crucial for the correct description of inner valence photoelectron peaks.
Dynamical Processes in Open Quantum Systems from a TDDFT Perspective: Resonances and Electron Photoemission
2015
We present a review of different computational methods to describe time-dependent phenomena in open quantum systems and their extension to a density-functional framework. We focus the discussion on electron emission processes in atoms and molecules addressing excited-state lifetimes and dissipative processes. Initially we analyze the concept of an electronic resonance, a central concept in spectroscopy associated with a metastable state from which an electron eventually escapes (electronic lifetime). Resonances play a fundamental role in many time-dependent molecular phenomena but can be rationalized from a time-independent context in terms of scattering states. We introduce the method of c…