11,261 research outputs found
Kohn-Sham calculations combined with an average pair-density functional theory
A recently developed formalism in which Kohn-Sham calculations are combined
with an ``average pair density functional theory'' is reviewed, and some new
properties of the effective electron-electron interaction entering in this
formalism are derived. A preliminary construction of a fully self-consitent
scheme is also presented in this framework.Comment: submitted to Int. J. Mod. Phys. B (proceedings of the 30th
International Workshop on Condensed Matter Theories
Propositional computability logic I
In the same sense as classical logic is a formal theory of truth, the
recently initiated approach called computability logic is a formal theory of
computability. It understands (interactive) computational problems as games
played by a machine against the environment, their computability as existence
of a machine that always wins the game, logical operators as operations on
computational problems, and validity of a logical formula as being a scheme of
"always computable" problems. The present contribution gives a detailed
exposition of a soundness and completeness proof for an axiomatization of one
of the most basic fragments of computability logic. The logical vocabulary of
this fragment contains operators for the so called parallel and choice
operations, and its atoms represent elementary problems, i.e. predicates in the
standard sense. This article is self-contained as it explains all relevant
concepts. While not technically necessary, however, familiarity with the
foundational paper "Introduction to computability logic" [Annals of Pure and
Applied Logic 123 (2003), pp.1-99] would greatly help the reader in
understanding the philosophy, underlying motivations, potential and utility of
computability logic, -- the context that determines the value of the present
results. Online introduction to the subject is available at
http://www.cis.upenn.edu/~giorgi/cl.html and
http://www.csc.villanova.edu/~japaridz/CL/gsoll.html .Comment: To appear in ACM Transactions on Computational Logi
London dispersion forces without density distortion: a path to first principles inclusion in density functional theory
We analyse a path to construct density functionals for the dispersion
interaction energy from an expression in terms of the ground state densities
and exchange-correlation holes of the isolated fragments. The expression is
based on a constrained search formalism for a supramolecular wavefunction that
is forced to leave the diagonal of the many-body density matrix of each
fragment unchanged, and is exact for the interaction between one-electron
densities. We discuss several aspects: the needed features a density functional
approximation for the exchange-correlation holes of the monomers should have,
the optimal choice of the one-electron basis needed (named "dispersals"), and
the functional derivative with respect to monomer density variations.Comment: 12 pages, 4 figure
The interaction-strength interpolation method for main-group chemistry: benchmarking, limitations, and perspectives
We have tested the original interaction-strength-interpolation (ISI)
exchange-correlation functional for main group chemistry. The ISI functional is
based on an interpolation between the weak and strong coupling limits and
includes exact-exchange as well as the G\"orling-Levy second-order energy. We
have analyzed in detail the basis-set dependence of the ISI functional, its
dependence on the ground-state orbitals, and the influence of the
size-consistency problem. We show and explain some of the expected limitations
of the ISI functional (i.e. for atomization energies), but also unexpected
results, such as the good performance for the interaction energy of
dispersion-bonded complexes when the ISI correlation is used as a correction to
Hartree-Fock.Comment: 20 pages, 20 figure
Decoherence-assisted transport and quantum criticalities
We study the dynamics of a two-level quantum system interacting with an
external environment that takes the form of an XY spin chain in the presence of
an external magnetic field. While the presence of the bath itself can enhance
the transition probability from the lower level to the upper level of the
system, we show that this noise-assisted phenomenon is sensitive to a change of
the quantum phase of the environment. The derivative of the transition
probability displays a maximum in correspondence with the critical value of the
applied field both in the case of isotropic and anisotropic chains
Winter precipitation and cyclones in the Mediterranean region: future climate scenarios in a regional simulation
Future climate projections show higher/lower winter (Dec-Jan-Feb) precipitation in the northern/southern Mediterranean region than in present climate conditions. This paper analyzes the results of regional model simulations of the A2 and B2 scenarios, which confirm this opposite precipitation change and link it to the change of cyclone activity. The increase of the winter cyclone activity in future climate scenarios over western Europe is responsible for the larger precipitation at the northern coast of the basin, though the bulk of the change is located outside the Mediterranean region. The reduction of cyclone activity inside the Mediterranean region in future scenarios is responsible for the lower precipitation at the southern and eastern Mediterranean coast
Spin Resolution of the Electron-Gas Correlation Energy: Positive same-spin contribution
The negative correlation energy per particle of a uniform electron gas of
density parameter and spin polarization is well known, but its
spin resolution into up-down, up-up, and down-down contributions is not.
Widely-used estimates are incorrect, and hamper the development of reliable
density functionals and pair distribution functions. For the spin resolution,
we present interpolations between high- and low-density limits that agree with
available Quantum Monte Carlo data. In the low-density limit for ,
we find that the same-spin correlation energy is unexpectedly positive, and we
explain why. We also estimate the up and down contributions to the kinetic
energy of correlation.Comment: new version, to appear in PRB Rapid Communicatio
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