1,161 research outputs found
The discontinuous nature of the exchange-correlation functional -- critical for strongly correlated systems
Standard approximations for the exchange-correlation functional have been
found to give big errors for the linearity condition of fractional charges,
leading to delocalization error, and the constancy condition of fractional
spins, leading to static correlation error. These two conditions are now
unified for states with both fractional charge and fractional spin: the exact
energy functional is a plane, linear along the fractional charge coordinate and
constant along the fractional spin coordinate with a line of discontinuity at
the integer. This sheds light on the nature of the derivative discontinuity and
calls for explicitly discontinuous functionals of the density or orbitals that
go beyond currently used smooth approximations. This is key for the application
of DFT to strongly correlated systems.Comment: 5 pages 2 figure
Localization and delocalization errors in density functional theory and implications for band-gap prediction
The band-gap problem and other systematic failures of approximate functionals
are explained from an analysis of total energy for fractional charges. The
deviation from the correct intrinsic linear behavior in finite systems leads to
delocalization and localization errors in large or bulk systems. Functionals
whose energy is convex for fractional charges such as LDA display an incorrect
apparent linearity in the bulk limit, due to the delocalization error. Concave
functionals also have an incorrect apparent linearity in the bulk calculation,
due to the localization error and imposed symmetry. This resolves an important
paradox and opens the possibility to obtain accurate band-gaps from DFT.Comment: 4 pages 4 figure
Broadening of the Derivative Discontinuity in Density Functional Theory
We clarify an important aspect of density functional theories, the broadening
of the derivative discontinuity (DD) in a quantum system, with fluctuating
particle number. Our focus is on a correlated model system, the single level
quantum dot in the regime of the Coulomb blockade. We find that the
DD-broadening is controlled by the small parameter , where
is the level broadening due to contacting and is a measure of the charging
energy. Our analysis suggests, that Kondoesque fluctuations have a tendency to
increase the DD-broadening, in our model by a factor of two.Comment: 4 pages, 2 figure
Global hybrids from the semiclassical atom theory satisfying the local density linear response
We propose global hybrid approximations of the exchange-correlation (XC)
energy functional which reproduce well the modified fourth-order gradient
expansion of the exchange energy in the semiclassical limit of many-electron
neutral atoms and recover the full local density approximation (LDA) linear
response. These XC functionals represent the hybrid versions of the APBE
functional [Phys. Rev. Lett. 106, 186406, (2011)] yet employing an additional
correlation functional which uses the localization concept of the correlation
energy density to improve the compatibility with the Hartree-Fock exchange as
well as the coupling-constant-resolved XC potential energy. Broad energetical
and structural testings, including thermochemistry and geometry, transition
metal complexes, non-covalent interactions, gold clusters and small
gold-molecule interfaces, as well as an analysis of the hybrid parameters, show
that our construction is quite robust. In particular, our testing shows that
the resulting hybrid, including 20\% of Hartree-Fock exchange and named hAPBE,
performs remarkably well for a broad palette of systems and properties, being
generally better than popular hybrids (PBE0 and B3LYP). Semi-empirical
dispersion corrections are also provided.Comment: 12 pages, 4 figure
Obliquity measurement and atmospheric characterization of the WASP-74 planetary system
We present new transit observations of the hot Jupiter WASP-74 b
( 1860 K) using the high-resolution spectrograph HARPS-N
and the multi-colour simultaneous imager MuSCAT2. We refine the orbital
properties of the planet and its host star, and measure its obliquity for the
first time. The measured sky-projected angle between the stellar spin-axis and
the planet's orbital axis is compatible with an orbit well-aligned with the
equator of the host star (). We are not
able to detect any absorption feature of H, or any other atomic
spectral features, in its high-resolution transmission spectra due to low S/N
at the line cores. Despite previous claims regarding the presence of strong
optical absorbers such TiO and VO gases in the atmosphere of WASP-74 b, the new
ground-based photometry combined with a reanalysis of previously reported
observations from the literature shows a slope in the low-resolution
transmission spectrum steeper than expected from Rayleigh scattering alone.Comment: Accepted for publication in Astronomy & Astrophysics. 12 pages, 8
figures, 5 table
The Hubbard model within the equations of motion approach
The Hubbard model has a special role in Condensed Matter Theory as it is
considered as the simplest Hamiltonian model one can write in order to describe
anomalous physical properties of some class of real materials. Unfortunately,
this model is not exactly solved except for some limits and therefore one
should resort to analytical methods, like the Equations of Motion Approach, or
to numerical techniques in order to attain a description of its relevant
features in the whole range of physical parameters (interaction, filling and
temperature). In this manuscript, the Composite Operator Method, which exploits
the above mentioned analytical technique, is presented and systematically
applied in order to get information about the behavior of all relevant
properties of the model (local, thermodynamic, single- and two- particle ones)
in comparison with many other analytical techniques, the above cited known
limits and numerical simulations. Within this approach, the Hubbard model is
shown to be also capable to describe some anomalous behaviors of the cuprate
superconductors.Comment: 232 pages, more than 300 figures, more than 500 reference
Mu-Opioid Receptors Transiently Activate the Akt-nNOS Pathway to Produce Sustained Potentiation of PKC-Mediated NMDAR-CaMKII Signaling
BACKGROUND: In periaqueductal grey (PAG) matter, cross-talk between the Mu-opioid receptor (MOR) and the glutamate N-methyl-D-Aspartate receptor (NMDAR)-CaMKII pathway supports the development of analgesic tolerance to morphine. In neurons, histidine triad nucleotide binding protein 1 (HINT1) connects the regulators of G protein signaling RGSZ1 and RGSZ2 to the C terminus of the MOR. In response to morphine, this HINT1-RGSZ complex binds PKCgamma, and afterwards, the interplay between PKCgamma, Src and Gz/Gi proteins leads to sustained potentiation of NMDAR-mediated glutamate responses. METHODOLOGY/PRINCIPAL FINDINGS: Following an intracerebroventricular (icv) injection of 10 nmol morphine, Akt was recruited to the synaptosomal membrane and activated by Thr308 and Ser473 phosphorylation. The Akt activation was immediately transferred to neural Nitric Oxide Synthase (nNOS) Ser1417. Afterwards, nitric oxide (NO)-released zinc ions recruited PKCgamma to the MOR to promote the Src-mediated phosphorylation of the Tyr1325 NMDAR2A subunit. This action increased NMDAR calcium flux and CaMKII was activated in a calcium-calmodulin dependent manner. CaMKII then acted on nNOS Ser847 to produce a sustained reduction in NO levels. The activation of the Akt-nNOS pathway was also reduced by the binding of these proteins to the MOR-HINT1 complex where they remained inactive. Tolerance to acute morphine developed as a result of phosphorylation of MOR cytosolic residues, uncoupling from the regulated G proteins which are transferred to RGSZ2 proteins. The diminished effect of morphine was prevented by LNNA, an inhibitor of nNOS function, and naltrindole, a delta-opioid receptor antagonist that also inhibits Akt. CONCLUSIONS/SIGNIFICANCE: Analysis of the regulatory phosphorylation of the proteins included in the study indicated that morphine produces a transient activation of the Akt/PKB-nNOS pathway. This activation occurs upstream of PKCgamma and Src mediated potentiation of NMDAR activity, ultimately leading to morphine tolerance. In summary, the Akt-nNOS pathway acts as a primer for morphine-triggered events which leads to the sustained potentiation of the NMDAR-CaMKII pathway and MOR inhibition
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