Modelling the electronic structure and magnetic properties of LiFeAs and FeSe using hybrid-exchange density functional theory

The electronic structure and magnetic properties of LiFeAs and FeSe have been studied using hybrid exchange density functional theory. The total energies for a unit cell in LiFeAs and FeSe with different spin states including non-magnetic and spin-2 are calculated. The spin-2 configuration has the lower energy for both LiFeAs and FeSe. The computed anti-ferromagnetic exchange interactions between spins on the nearest (next nearest) neighbouring Fe atoms in LiFeAs and FeSe are approximately 14 (17) meV and 6 (13) meV respectively. The total energies of the checkerboard and stripe-type anti-ferromagnetic ordering for LiFeAs and FeSe are compared, yielding that for LiFeAs the checkerboard is lower whereas for FeSe the stripe-type is lower. However, owing to the fact that the exchange interaction of the next nearest neighbour is larger than that of the nearest one, which means that the collinear ordering might be the ground state. These results are in agreement with previous theoretical calculations and experiments. Especially the calculations for LiFeAs indicate a co-existence of conducting d-bands at the Fermi surface and d-orbital magnetism far below the Fermi surface. The theoretical results presented here might be useful for the experimentalists working on the electronic structure and magnetism of iron-based superconductors.Comment: 7 pages, 4 figures, 1 table, accepted by Solid State Communication

Strain-Driven Mn-Reorganization in Overlithiated LixMn2O4 Epitaxial Thin-Film Electrodes

Lithium manganate LixMn2O4 (LMO) is a lithium ion cathode that suffers from the widely observed but poorly understood phenomenon of capacity loss due to Mn dissolution during electrochemical cycling. Here, operando X-ray reflectivity (low- and high-angle) is used to study the structure and morphology of epitaxial LMO (111) thin film cathodes undergoing lithium insertion and extraction to understand the inter-relationships between biaxial strain and Mn-dissolution. The initially strain-relieved LiMn2O4 films generate in-plane tensile and compressive strains for delithiated (x 1) charge states, respectively. The results reveal reversible Li insertion into LMO with no measurable Mn-loss for 0 1) reveals Mn loss from LMO along with dramatic changes in the intensity of the (111) Bragg peak that cannot be explained by Li stoichiometry. These results reveal a partially reversible site reorganization of Mn ions within the LMO film that is not seen in bulk reactions and indicates a transition in Mn-layer stoichiometry from 3:1 to 2:2 in alternating cation planes. Density functional theory calculations confirm that compressive strains (at x = 2) stabilize LMO structures with 2:2 Mn site distributions, therefore providing new insights into the role of lattice strain in the stability of LMO

Uniform electron gases

We show that the traditional concept of the uniform electron gas (UEG) --- a homogeneous system of finite density, consisting of an infinite number of electrons in an infinite volume --- is inadequate to model the UEGs that arise in finite systems. We argue that, in general, a UEG is characterized by at least two parameters, \textit{viz.} the usual one-electron density parameter $\rho$ and a new two-electron parameter $\eta$. We outline a systematic strategy to determine a new density functional $E(\rho,\eta)$ across the spectrum of possible $\rho$ and $\eta$ values.Comment: 8 pages, 2 figures, 5 table

Does Al4H14— cluster anion exist? High-level ab initio study

A comprehensive ab initio investigation using coupled cluster theory with the aug-cc-pVnZ, n = D,T basis sets is carried out to identify distinct structures of the Al4H14— cluster anion and to evaluate its fragmentation stability. Both thermodynamic and mechanistic aspects of the fragmentation reactions are studied. The observation of this so far the most hydrogenated aluminum tetramer was reported in the recent mass spectrometry study of Li et al. (2010) J Chem Phys 132:241103–241104. The four Al4H14— anion structures found are chain-like with the multiple-coordinate Al center and can be viewed approximately as comprising Al2H7— and Al2H7 moieties. Locating computationally some of the Al4H14— minima on the correlated ab initio potential energy surfaces required the triple-zeta quality basis set to describe adequately the Al multi-coordinate bonding. For the two most stable Al4H14— isomers, the mechanism of their low-barrier interconversion is described. The dissociation of Al4H14— into the Al2H7— and Al2H7 units is predicted to require 20-22 (10-13) kcal mol-1 in terms of ΔH (ΔG) estimated at T = 298.15 K and p = 1 atm. However, Al4H14— is found to be a metastable species in the gas phase: the H2 loss from the radical moiety of its most favorable isomer is exothermic by 18 kcal mol-1 in terms of ΔH (298.15 K) and by 25 kcal mol-1 in terms of ΔG(298.15 K), with the enthalpic/free energy barrier involved being less than 1 kcal mol-1. By contrast with alane Al4H14—, only a weakly bound complex between Ga4H12— and H2 has been identified for the gallium analogue using the relativistic effective core potential

Consequence of one-electron oxidation and one-electron reduction for aniline

Quantum-chemical calculations were performed for all possible isomers of neutral aniline and its redox forms, and intramolecular proton-transfer (prototropy) accompanied by π-electron delocalization was analyzed. One-electron oxidation (PhNH2 – e → [PhNH2]+•) has no important effect on tautomeric preferences. The enamine tautomer is preferred for oxidized aniline similarly as for the neutral molecule. Dramatical changes take place when proceeding from neutral to reduced aniline. One-electron reduction (PhNH2 + e → [PhNH2]-•) favors the imine tautomer. Independently on the state of oxidation, π- and n-electrons are more delocalized for the enamine than imine tautomers. The change of the tautomeric preferences for reduced aniline may partially explain the origin of the CH tautomers for reduced nucleobases (cytosine, adenine, and guanine)

Calculation of molecular thermochemical data and their availability in databases

Thermodynamic properties of molecules can be obtained by experiment, by statistical mechanics in conjunction with electronic structure theory and by empirical rules like group additivity. The latter two methods are briefly re-viewed in this chapter. The overview of electronic structure methods is intended for readers less experienced in electronic structure theory and focuses on concepts without going into mathematical details. This is followed by a brief description of group additivity schemes; finally, an overview of databases listing reliable thermochemical data is given

Sequencing and functional annotation of avian pathogenic Escherichia coli serogroup O78 strains reveals the evolution of E. coli lineages pathogenic for poultry via distinct mechanisms

Avian pathogenic Escherichia coli (APEC) causes respiratory and systemic disease in poultry. Sequencing of a multilocus sequence type 95 (ST95) serogroup O1 strain previously indicated that APEC resembles E. coli causing extraintestinal human diseases. We sequenced the genomes of two strains of another dominant APEC lineage (ST23 serogroup O78 strains χ7122 and IMT2125) and compared them to each other and to the reannotated APEC O1 sequence. For comparison, we also sequenced a human enterotoxigenic E. coli (ETEC) strain of the same ST23 serogroup O78 lineage. Phylogenetic analysis indicated that the APEC O78 strains were more closely related to human ST23 ETEC than to APEC O1, indicating that separation of pathotypes on the basis of their extraintestinal or diarrheagenic nature is not supported by their phylogeny. The accessory genome of APEC ST23 strains exhibited limited conservation of APEC O1 genomic islands and a distinct repertoire of virulence-associated loci. In light of this diversity, we surveyed the phenotype of 2,185 signature-tagged transposon mutants of χ7122 following intra-air sac inoculation of turkeys. This procedure identified novel APEC ST23 genes that play strain- and tissue-specific roles during infection. For example, genes mediating group 4 capsule synthesis were required for the virulence of χ7122 and were conserved in IMT2125 but absent from APEC O1. Our data reveal the genetic diversity of E. coli strains adapted to cause the same avian disease and indicate that the core genome of the ST23 lineage serves as a chassis for the evolution of E. coli strains adapted to cause avian or human disease via acquisition of distinct virulence genes

Human Apolipoprotein A-I-Derived Amyloid: Its Association with Atherosclerosis

Amyloidoses constitute a group of diseases in which soluble proteins aggregate and deposit extracellularly in tissues. Nonhereditary apolipoprotein A-I (apoA-I) amyloid is characterized by deposits of nonvariant protein in atherosclerotic arteries. Despite being common, little is known about the pathogenesis and significance of apoA-I deposition. In this work we investigated by fluorescence and biochemical approaches the impact of a cellular microenvironment associated with chronic inflammation on the folding and pro-amyloidogenic processing of apoA-I. Results showed that mildly acidic pH promotes misfolding, aggregation, and increased binding of apoA-I to extracellular matrix elements, thus favoring protein deposition as amyloid like-complexes. In addition, activated neutrophils and oxidative/proteolytic cleavage of the protein give rise to pro amyloidogenic products. We conclude that, even though apoA-I is not inherently amyloidogenic, it may produce non hereditary amyloidosis as a consequence of the pro-inflammatory microenvironment associated to atherogenesis