Full potential LAPW calculation of electron momentum density and related properties of Li

Electron momentum density and Compton profiles in Lithium along $$,$$, and $$ directions are calculated using Full-Potential Linear Augmented Plane Wave basis within generalized gradient approximation. The profiles have been corrected for correlations with Lam-Platzman formulation using self-consistent charge density. The first and second derivatives of Compton profiles are studied to investigate the Fermi surface breaks. Decent agreement is observed between recent experimental and our calculated values. Our values for the derivatives are found to be in better agreement with experiments than earlier theoretical results. Two-photon momentum density and one- and two-dimensional angular correlation of positron annihilation radiation are also calculated within the same formalism and including the electron-positron enhancement factor.Comment: 11 pages, 7 figures TO appear in Physical Review

Molecular Interpretation of ACTH-β-Endorphin Coaggregation: Relevance to Secretory Granule Biogenesis

Peptide/protein hormones could be stored as non-toxic amyloid-like structures in pituitary secretory granules. ACTH and β-endorphin are two of the important peptide hormones that get co-stored in the pituitary secretory granules. Here, we study molecular interactions between ACTH and β-endorphin and their colocalization in the form of amyloid aggregates. Although ACTH is known to be a part of ACTH-β-endorphin aggregate, ACTH alone cannot aggregate into amyloid under various plausible conditions. Using all atom molecular dynamics simulation we investigate the early molecular interaction events in the ACTH-β-endorphin system, β-endorphin-only system and ACTH-only system. We find that β-endorphin and ACTH formed an interacting unit, whereas negligible interactions were observed between ACTH molecules in ACTH-only system. Our data suggest that ACTH is not only involved in interaction with β-endorphin but also enhances the stability of mixed oligomers of the entire system

Positron lifetimes and phase transitions in solids

Lifetimes of positrons annihilating in NH<SUB>4</SUB>Cl and in nitrate glasses have been measured as a function of temperature. The observed temperature dependence of tau<SUB>2</SUB> and I<SUB>2</SUB> indicates that the I<SUB>2</SUB> is significantly affected by changes in molar volumes accompanying the phase transitions in these solids. I<SUB>2</SUB> varies in the same direction as the molar volume thus underlining the role of free volume in the positron annihilation process in condensed media

Positro annihilation in organic media and ionic crystals

The lifetimes of the long-lived comonents τ<SUB>2</SUB> in positron annihilation in organic media are found to depend upon the first ionization potentials of the molecules. In alkali halides τ<SUB>2</SUB> is related to the ratio of the volume of the anion to that of the interstitial void

Positron lifetime studies in organic media

Lifetimes of positrons annihilating in a number of organic compounds consisting of aromatic hydrocarbons, substituted benzenes, phenols, anilines and ketones have been measured. Experimentally measured values of tau2 and I2 are examined to determine whether positron annihilation takes place at a particular site of the molecule or whether it depends on average properties of the molecules. The intensity I2 seems to be related to the width of Ore gap in organic molecules; the tau2 values in molecular liquids, however, can be interpreted in terms of additive atomic contributions to pick-off quenching. In substituted benzenes the results show changes due to substituent effects and these changes could be correlated with Hammett's sigma-constant. Results indicate that positron annihilation in organic media is determined by microscopic properties of the molecules such as ionization potentials (or width of Ore gap) and electron densities at the annihilation sites

<SUP>151</SUP>Eu and <SUP>57</SUP>Fe M&#246;ssbauer studies of EuCoO<SUB>3</SUB>

151Eu and 57Fe M&#246;ssbauer spectra of EuCoO3 have been recorded in the 78-1200 K temperature range. The spectra along with magnetic susceptibility, X-ray diffraction and other measurements have been employed to understand the electronic and magnetic properties of EuCoO3. The studies are consistent with Goodenough's description of the electronic properties of LaCoO3

Effect of the rare earth ion on the spin state equilibria in perovskite rare earth metal cobaltates. Yttrium trioxocobaltate(III) and erbium trioxocobaltate(III)

The relative proportions of high-spin Co3+ and low-spin CoIII in HoCoO3 are about 1:1 at temperatures above 300 K, while in the lighter rare earth metal cobaltates, there is evidence for appreciable charge-transfer from Co3+ to CoIII producing intermediate states. We have investigated the effect of the size of the rare earth metal ion on the electronic and magnetic properties of cobaltates by examining YCoO3 and ErCoO3 in some detail. Mössbauer studies show that the properties of YCoO3 are similar to those of the lighter rare earth metal cobaltates in that there is considerable electron transfer from Co3+ to CoIII giving rise to intermediate charge-transfer states. However, ErCoO3 is quite similar to HoCoO3 with no evidence for electron transfer and both χgT and Mössbauer data show an essentially constant Co3+/CoIII ratio. Both YCoO3 and ErCoO3 show a first order localized electron-itinerant electron transition around 1200 K above which the bonding eg electrons form σ∗ bands