Exchange and correlation as a functional of the local density of states

A functional $E_{xc}[\rho(\r,\epsilon)]$ is presented, in which the exchange and correlation energy of an electron gas depends on the local density of occupied states. A simple local parametrization scheme is proposed, entirely from first principles, based on the decomposition of the exchange-correlation hole in scattering states of different relative energies. In its practical Kohn-Sham-like form, the single-electron orbitals become the independent variables, and an explicit formula for the functional derivative is obtained.Comment: 5 pages. Expanded version. Will appear in Phys. Rev.

Silk Road: A Journal of Eurasian Development – Prospectus and Purpose

This editorial explains the beginnings of the journal Silk Road commencing around the time of the 2019 Tashkent agreement and the journal’s future scope and ambitions. As nations within Central Asia look towards greater cooperation the editors articulate the journal’s focus on public policy issues and how Silk Road intends to offer a long-held need for scholarly perspectives and analysis from within the region itself. It explains how the journal’s name links to the past of the region, to evoke its ‘inclusive’ connotations as a space of exchange, travel and ‘ambiguity’ but also is ‘intended to evoke a dynamic forward look towards the future’. Embodying a broad and interdisciplinary focus in its scope, it is hoped that the journal’s name also paves the way to its long term mission of encouraging ‘creativity among researchers working’ on policy in the region and to ‘prompt them both to analyse current public policy and to imagine its future’

Fiberoptisch unterstützte endotracheale Intubation durch die Larynxmaske im Kindesalter

Zusammenfassung: Die fiberoptisch assistierte endotracheale Intubation durch die Larynxmaske ist ein sicheres Verfahren, um beim pädiatrischen Patienten mit unerwarteter sowie auch bei bekannter schwieriger Intubation den Atemweg einfach und zuverlässig zu sichern. Die Methode stellt eine Standardtechnik in der Atemwegssicherung dar; sie muss einerseits Bestandteil der klinischen Ausbildung sein und andererseits regelmäßig trainiert werden. Das Entfernen der Larynxmaske über den Endotrachealtubus wird durch dessen kurze Länge erschwert bzw. der Endotrachealtubus kann dabei sehr leicht aus der Trachea dislozieren. Nebst einer Vielzahl von Techniken, die Larynxmaske sicher über den Endotrachealtubus zu entfernen, bietet der Cook Airway Exchange Catheter in der Kinderanästhesie eine einfache Methode, nicht nur die Larynxmaske sicher über den Tubus zu entfernen, sondern anschließend auch den geeigneten Tubus einzuführen. Dies ist insbesondere bei gecufften Tuben wünschenswert, bei denen der Pilotballon des gecufften Tubus zu groß ist, um Larynxmasken der Größen 2,5 und kleiner zu passieren. Die vorliegende Arbeit zeigt schrittweise die fiberoptisch assistierte endotracheale Intubation durch die Larynxmaske beim Kind und diskutiert ihre Bedeutung. Eine Liste mit aufeinanderabgestimmten Größen von Larynxmasken, Endotrachealtuben und Airway Exchange Cathetern ist ebenfalls enthalte

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 $r_s$ and spin polarization $\zeta$ 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 $\zeta = 0$, 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

Theoretical analysis of magnetic coupling in sandwich clusters V_n(C_6H_6)_{n+1}

The mechanism of ferromagnetism stability in sandwich clusters V$_n$(C$_6$H$_6$)$_{n+1}$ has been studied by first-principles calculation and model analysis. It is found that each of the three types of bonds between V and benzene (Bz) plays different roles. V 3d$_{z^2}$ orbital, extending along the molecular axis, is weakly hybridized with Bz's HOMO-1 orbital to form the $\sigma$-bond. It is quite localized and singly occupied, which contributes 1$\mu_B$ to the magnetic moment but little to the magnetic coupling of neighboring V magnetic moments. The in-plane d$_{x^2-y^2}$, d$_{xy}$ orbitals are hybridized with the LUMO of Bz and constitute the $\delta$-bond. This hybridization is medium and crucial to the magnetic coupling though the $\delta$ states have no net contribution to the total magnetic moment. d$_{xz}$, d$_{yz}$ and HOMO of Bz form a quite strong $\pi$-bond to hold the molecular structure but they are inactive in magnetism because their energy levels are far away from the Fermi level. Based on the results of first-principles calculation, we point out that the ferromagnetism stability is closely related with the mechanism proposed by Kanamori and Terakura [J. Kanamori and K. Terakura, J. Phys. Soc. Jpn. 70, 1433 (2001)]. However, the presence of edge Bz's in the cluster introduces an important modification. A simple model is constructed to explain the essence of the physical picture.Comment: 16 pages, 7 figure

Performance of the modified Becke-Johnson potential

Very recently, in the 2011 version of the Wien2K code, the long standing shortcome of the codes based on Density Functional Theory, namely, its impossibility to account for the experimental band gap value of semiconductors, was overcome. The novelty is the introduction of a new exchange and correlation potential, the modified Becke-Johnson potential (mBJLDA). In this paper, we report our detailed analysis of this recent work. We calculated using this code, the band structure of forty one semiconductors and found an important improvement in the overall agreement with experiment as Tran and Blaha [{\em Phys. Rev. Lett.} 102, 226401 (2009)] did before for a more reduced set of semiconductors. We find, nevertheless, within this enhanced set, that the deviation from the experimental gap value can reach even much more than 20%, in some cases. Furthermore, since there is no exchange and correlation energy term from which the mBJLDA potential can be deduced, a direct optimization procedure to get the lattice parameter in a consistent way is not possible as in the usual theory. These authors suggest that a LDA or a GGA optimization procedure is used previous to a band structure calculation and the resulting lattice parameter introduced into the 2011 code. This choice is important since small percentage differences in the lattice parameter can give rise to quite higher percentage deviations from experiment in the predicted band gap value.Comment: 10 pages, 2 figures, 5 Table

Self-reported empathy in adult women with Autism Spectrum Disorders:A systematic mini review

IntroductionThere is limited research on Autism Spectrum Disorders (ASD) in females. Although the empathy construct has been examined thoroughly in autism, little attention has been paid to empathy in adult women with this condition or to gender differences within the disorder.ObjectiveSelf-reported empathy in adult women with ASD was examined and compared to that of typically developed men and women as well as to men with this condition.MethodsOnline databases were searched for articles investigating self-reported empathy among adult women with ASD. Only six studies comparing women to men were identified.ResultsAll studies found women with an ASD to report lower levels of empathy than typically developed women, and typically developed men, but similar levels to men with this condition.ConclusionThe self-reported empathic ability of women diagnosed with ASD resembles that of their male counterparts most closely; they show a hypermasculinisation in empathy. This is particularly surprising considering the large gender difference in empathy in the general population.DiscussionOne of the limitations of this review is that the current diagnostic criteria for ASD are oriented towards male-specific behaviour and fail to integrate gender specific characteristics. Hence, women diagnosed with ASD are likely to be at the male end of the continuum. The suggested hypermasculinisation of women on the spectrum, as evident from this review, may therefore be exaggerated due to a selection bias

Comparative study of density functional theories of the exchange-correlation hole and energy in silicon

We present a detailed study of the exchange-correlation hole and exchange-correlation energy per particle in the Si crystal as calculated by the Variational Monte Carlo method and predicted by various density functional models. Nonlocal density averaging methods prove to be successful in correcting severe errors in the local density approximation (LDA) at low densities where the density changes dramatically over the correlation length of the LDA hole, but fail to provide systematic improvements at higher densities where the effects of density inhomogeneity are more subtle. Exchange and correlation considered separately show a sensitivity to the nonlocal semiconductor crystal environment, particularly within the Si bond, which is not predicted by the nonlocal approaches based on density averaging. The exchange hole is well described by a bonding orbital picture, while the correlation hole has a significant component due to the polarization of the nearby bonds, which partially screens out the anisotropy in the exchange hole.Comment: 16 pages, 5 figures, RevTeX, added conten

Density Functional Theory Approach to Noncovalent Interactions via Interacting Monomer Densities

A recently proposed "DFT+dispersion" treatment (Rajchel et al., Phys. Rev. Lett., 2010, 104, 163001) is described in detail and illustrated by more examples. The formalism derives the dispersion-free density functional theory (DFT) interaction energy and combines it with the dispersion energy from separate DFT calculations. It consists in the self-consistent polarization of DFT monomers restrained by the exclusion principle via the Pauli blockade technique. Within the monomers a complete exchange-correlation potential should be used, but between them only the exact exchange operates. The applications to wide range of molecular complexes from rare-gas dimers to H-bonds to pi-electron interactions show good agreement with benchmark values.Comment: 9 pages, 5 figures, 2 tables, REVTeX