4,905 research outputs found
Density functional theory for strongly interacting electrons
We present an alternative to the Kohn-Sham formulation of density functional
theory for the ground-state properties of strongly interacting electronic
systems. The idea is to start from the limit of zero kinetic energy and
systematically expand the universal energy functional of the density in powers
of a "coupling constant" that controls the magnitude of the kinetic energy. The
problem of minimizing the energy is reduced to the solution of a strictly
correlated electron problem in the presence of an effective potential, which
plays in our theory the same role that the Kohn-Sham potential plays in the
traditional formulation. We discuss several schemes for approximating the
energy functional, and report preliminary results for low-density quantum dots.Comment: Revised version, to appear in Phys. Rev. Let
Sequential Flavour Symmetry Breaking
The gauge sector of the Standard Model (SM) exhibits a flavour symmetry which
allows for independent unitary transformations of the fermion multiplets. In
the SM the flavour symmetry is broken by the Yukawa couplings to the Higgs
boson, and the resulting fermion masses and mixing angles show a pronounced
hierarchy. In this work we connect the observed hierarchy to a sequence of
intermediate effective theories, where the flavour symmetries are broken in a
step-wise fashion by vacuum expectation values of suitably constructed spurion
fields. We identify the possible scenarios in the quark sector and discuss some
implications of this approach.Comment: 22 pages latex, no figure
First-principles calculations and bias-dependent STM measurements at the alpha-Sn/Ge(111) surface: a clear indication for the 1U2D configuration
The nature of the alpha-Sn/Ge(111) surface is still a matter of debate. In
particular, two possible configurations have been proposed for the 3x3 ground
state of this surface: one with two Sn adatoms in a lower position with respect
to the third one (1U2D) and the other with opposite configuration (2U1D). By
means of first-principles quasiparticle calculations we could simulate STM
images as a function of bias voltage and compare them with STM experimental
results at 78K, obtaining an unambiguous indication that the stable
configuration for the alpha-Sn/Ge(111) surface is the 1U2D. The possible
inequivalence of the two down Sn adatoms is also discussed.Comment: Submitted to PR
Quaternionic Toric Manifolds
In the present paper we introduce and study a new notion of toric manifold in the quaternionic setting. We develop a construction with which, starting from appropriate m-dimensional Delzant polytopes, we obtain manifolds of real dimension 4m, acted on by m copies of the group Sp(1) of unit quaternions. These manifolds are quaternionic regular and can be endowed with a 4-plectic structure and a generalized moment map. Convexity properties of the image of the moment map are studied. Quaternionic toric manifolds appear to be a large enough class of examples where one can test and study new results in quaternionic geometry
On Compact Affine Quaternionic Curves and Surfaces
This paper is devoted to the study of affine quaternionic manifolds and to a possible classification of all compact affine quater- nionic curves and surfaces. It is established that on an affine quater- nionic manifold there is one and only one affine quaternionic structure. A direct result, based on the celebrated Kodaira Theorem that classifies all compact complex manifolds in complex dimension 2, states that the only compact affine quaternionic curves are the quaternionic tori. As for compact affine quaternionic surfaces, the study of their fundamental groups, together with the inspection of all nilpotent hypercomplex sim- ply connected 8-dimensional Lie Groups, identifies a path towards their classification
Adiabatic connection at negative coupling strengths
The adiabatic connection of density functional theory (DFT) for electronic
systems is generalized here to negative values of the coupling strength
(with {\em attractive} electrons). In the extreme limit
a simple physical solution is presented and its implications
for DFT (as well as its limitations) are discussed. For two-electron systems (a
case in which the present solution can be calculated exactly), we find that an
interpolation between the limit and the opposite limit of
infinitely strong repulsion () yields a rather accurate
estimate of the second-order correlation energy E\cor\glt[\rho] for several
different densities , without using virtual orbitals. The same procedure
is also applied to the Be isoelectronic series, analyzing the effects of
near-degeneracy.Comment: 9 pages, submitted to PR
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