263 research outputs found
Density-functional theory of nonequilibrium tunneling
Nanoscale optoelectronics and molecular-electronics systems operate with
current injection and nonequilibrium tunneling, phenomena that challenge
consistent descriptions of the steady-state transport. The current affects the
electron-density variation and hence the inter- and intra-molecular bonding
which in turn determines the transport magnitude. The standard approach for
efficient characterization of steady-state tunneling combines ground-state
density functional theory (DFT) calculations (of an effective scattering
potential) with a Landauer-type formalism and ignores all actual many-body
scattering. The standard method also lacks a formal variational basis. This
paper formulates a Lippmann-Schwinger collision density functional theory
(LSC-DFT) for tunneling transport with full electron-electron interactions.
Quantum-kinetic (Dyson) equations are used for an exact reformulation that
expresses the variational noninteracting and interacting many-body scattering
T-matrices in terms of universal density functionals. The many-body
Lippmann-Schwinger (LS) variational principle defines an implicit equation for
the exact nonequilibrium density.Comment: Title, abstract, and text are adjusted to precise formulations (the
original version contained a logical error
Nonequilibrium thermodynamics of interacting tunneling transport: variational grand potential, density-functional formulation, and nature of steady-state forces
The standard formulation of tunneling transport rests on an open-boundary
modeling. There, conserving approximations to nonequilibrium Green function or
quantum-statistical mechanics provide consistent but computational costly
approaches; alternatively, use of density-dependent ballistic-transport
calculations [e.g., Phys. Rev. B 52, 5335 (1995)], here denoted `DBT', provide
computationally efficient (approximate) atomistic characterizations of the
electron behavior but has until now lacked a formal justification. This paper
presents an exact, variational nonequilibrium thermodynamic theory for fully
interacting tunneling and provides a rigorous foundation for frozen-nuclei DBT
calculations as a lowest order approximation to an exact nonequilibrium
thermodynamics density functional evaluation. The theory starts from the
complete electron nonequilibrium quantum statistical mechanics and I identify
the operator for the nonequilibrium Gibbs free energy. I demonstrate a minimal
property of a functional for the nonequilibrium thermodynamic grand potential
which thus uniquely identifies the solution as the exact nonequilibrium density
matrix. I also show that a uniqueness-of-density proof from a closely related
study [Phys. Rev. B 78, 165109 (2008)] makes it possible to provide a
single-particle formulation based on universal electron-density functionals. I
illustrate a formal evaluation of the thermodynamics grand potential value
which is closely related to the variation in scattering phase shifts and hence
to Friedel density oscillations. This paper also discusses the difference
between the here-presented exact thermodynamics forces and the often-used
electrostatic forces. Finally the paper documents an inherent adiabatic nature
of the thermodynamics forces and observes that these are suited for a
nonequilibrium implementation of the Born-Oppenheimer approximation.Comment: 37 pages, 3 Figure
View From Outside the Viewing Sphere
The âviewing sphereâ, as defined by Euclid and explored by Gibson as the âoptic arrayâ, is generally thought of as wrapped around the eye. Can an observer step out of it? With currently popular photographic techniques, the spectator is forced to, because the viewing sphere is presented as a pictorial object. Then the question is whether human observers are able to use such pictorial representations in an intuitive manner. Can the spectator âmentally step into the interiorâ of the pictorial viewing sphere? We explore this issue in a short experiment. Perhaps unsurprisingly, because the eye cannot see itself, the short answer is no
The roots of "Western European societal evolution". A concept of Europe by JenĆ SzƱcs
JenĆ SzƱcs wrote his essay entitled Sketch on the three regions of Europe in the early 1980s in Hungary. During these years, a historically well-argued opinion emphasising a substantial difference between Central European and Eastern European societies was warmly received in various circles of the political opposition. In a wider European perspective SzƱcs used the old âliberty toposâ which claims that the history of Europe is no other than the fulfillment of liberty. In his Sketch, SzƱcs does not only concentrate on questions concerning the Middle Ages in Western Europe. Yet it is this stream of thought which brought a new perspective to explaining European history. His picture of the Middle Ages represents well that there is a way to integrate all typical Western motifs of post-war self-definition into a single theory. Mainly, the âliberty motifâ, as a sign of âEuropeanismâ â in the interpretation of BibĂłâs concept, Anglo-saxon Marxists and Weberâs social theory â, developed from medieval concepts of state and society and from an analysis of economic and social structures. SzƱcsâs historical aspect was a typical intellectual product of the 1980s: this was the time when a few Central European historians started to outline non-Marxist aspects of social theory and categories of modernisation theories, but concealing them with Marxist terminology
The Long Shadow of History. Roman Legacy and Economic Development -- Evidence from the German Limes
- âŠ