11,139 research outputs found

### Nearsightedness of Electronic Matter

In an earlier paper, W. Kohn had qualitatively introduced the concept of
"nearsightedness" of electrons in many-atom systems. It can be viewed as
underlying such important ideas as Pauling's "chemical bond," "transferability"
and Yang's computational principle of "divide and conquer." It describes the
fact that, for fixed chemical potential, local electronic properties, like the
density $n(r)$, depend significantly on the effective external potential only
at nearby points. Changes of that potential, {\it no matter how large}, beyond
a distance $\textsf{R}$ have {\it limited} effects on local electronic
properties, which rapidly tend to zero as function of $\textsf{R}$. In the
present paper, the concept is first sharpened for representative models of
uncharged fermions moving in external potentials, followed by a discussion of
the effects of electron-electron interactions and of perturbing external
charges.Comment: final for

### Edge Electron Gas

The uniform electron gas, the traditional starting point for density-based
many-body theories of inhomogeneous systems, is inappropriate near electronic
edges. In its place we put forward the appropriate concept of the edge electron
gas.Comment: 4 pages RevTex with 7 ps-figures included. Minor changes in
title,text and figure

### Quantal Density Functional Theory of Degenerate States

The treatment of degenerate states within Kohn-Sham density functional theory
(KS-DFT) is a problem of longstanding interest. We propose a solution to this
mapping from the interacting degenerate system to that of the noninteracting
fermion model whereby the equivalent density and energy are obtained via the
unifying physical framework of quantal density functional theory (Q-DFT). We
describe the Q-DFT of \textit{both} ground and excited degenerate states, and
for the cases of \textit{both} pure state and ensemble v-representable
densities. This then further provides a rigorous physical interpretation of the
density and bidensity energy functionals, and of their functional derivatives,
of the corresponding KS-DFT. We conclude with examples of the mappings within
Q-DFT.Comment: 10 pages. minor changes made. to appear in PR

### A generic multibody simulation

Described is a dynamic simulation package which can be configured for orbital test scenarios involving multiple bodies. The rotational and translational state integration methods are selectable for each individual body and may be changed during a run if necessary. Characteristics of the bodies are determined by assigning components consisting of mass properties, forces, and moments, which are the outputs of user-defined environmental models. Generic model implementation is facilitated by a transformation processor which performs coordinate frame inversions. Transformations are defined in the initialization file as part of the simulation configuration. The simulation package includes an initialization processor, which consists of a command line preprocessor, a general purpose grammar, and a syntax scanner. These permit specifications of the bodies, their interrelationships, and their initial states in a format that is not dependent on a particular test scenario

### Resistivity and optical conductivity of cuprates within the t-J model

The optical conductivity $\sigma(\omega)$ and the d.c. resistivity $\rho(T)$
within the extended t-J model on a square lattice, as relevant to high-$T_c$
cuprates, are reinvestigated using the exact-diagonalization method for small
systems, improved by performing a twisted boundary condition averaging. The
influence of the next-nearest-neighbor hopping $t'$ is also considered. The
behaviour of results at intermediate doping is consistent with a
marginal-Fermi-liquid scenario and in the case of $t'=0$ for $\omega>T$ follows
the power law $\sigma \propto \omega^{-\nu}$ with $\nu \sim 0.65$ consistent
with experiments. At low doping $c_h<0.1$ for $T<J$ $\sigma(\omega)$ develops a
shoulder at $\omega\sim \omega^*$, consistent with the observed mid-infrared
peak in experiments, accompanied by a shallow dip for $\omega < \omega^*$. This
region is characterized by the resistivity saturation, whereas a more coherent
transport appears at $T < T^*$ producing a more pronounced decrease in
$\rho(T)$. The behavior of the normalized resistivity $c_h \rho(T)$ is within a
factor of 2 quantitatively consistent with experiments in cuprates.Comment: 8 pages, 10 figure

### Generalization of the density-matrix method to a non-orthogonal basis

We present a generalization of the Li, Nunes and Vanderbilt density-matrix
method to the case of a non-orthogonal set of basis functions. A representation
of the real-space density matrix is chosen in such a way that only the overlap
matrix, and not its inverse, appears in the energy functional. The generalized
energy functional is shown to be variational with respect to the elements of
the density matrix, which typically remains well localized.Comment: 11 pages + 2 postcript figures at the end (search for -cut here

### The Decay Properties of the Finite Temperature Density Matrix in Metals

Using ordinary Fourier analysis, the asymptotic decay behavior of the density
matrix F(r,r') is derived for the case of a metal at a finite electronic
temperature. An oscillatory behavior which is damped exponentially with
increasing distance between r and r' is found. The decay rate is not only
determined by the electronic temperature, but also by the Fermi energy. The
theoretical predictions are confirmed by numerical simulations

### Theory of the Stark Effect for P donors in Si

We develop a multi-valley effective mass theory for substitutional donors in
silicon in an inhomogeneous environment. Valley-orbit coupling is treated
perturbatively. We apply the theory to the Stark effect in Si:P. The method
becomes more accurate at high fields, and it is designed to give correct
experimental binding energies at zero field. Unexpectedly, the ground state
energy for the donor electron is found to increase with electric field as a
consequence of spectrum narrowing of the 1s manifold. Our results are of
particular importance for the Kane quantum computer.Comment: published versio

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