9,272 research outputs found
Band structure and atomic sum rules for x-ray dichroism
Corrections to the atomic orbital sum rule for circular magnetic x-ray
dichroism in solids are derived using orthonormal LMTOs as a single-particle
basis for electron band states.Comment: 7 pages, no figure
Insights from ARPES for an undoped, four-layered, two-gap high-T_c superconductor
An undoped cuprate with apical fluorine and inner (i) and outer (o)
CuO2-layers is a 60 K superconductor whose Fermi surface (FS) has large n- and
p-doped sheets with the SC gap on the n-sheet twice that on the p -sheet (Y.
Chen et al.). The Fermi surface is not reproduced by the LDA, but the screening
must be substantially reduced due to electronic correlations, and oxygen in the
o-layers must be allowed to dimple outwards. This charges the i-layers by
0.01|e|, causes an 0.4 eV Madelung-potential difference between the i and o
-layers, quenches the i-o hopping, and localizes the n-sheets onto the
i-layers, thus protecting their d-wave pairs from being broken by scattering on
impurities in the BaF layers. The correlation-reduced screening strengthens the
coupling to z-axis phonons.Comment: 4 pages, 3 figure
Multiplet ligand-field theory using Wannier orbitals
We demonstrate how ab initio cluster calculations including the full Coulomb
vertex can be done in the basis of the localized, generalized Wannier orbitals
which describe the low-energy density functional (LDA) band structure of the
infinite crystal, e.g. the transition metal 3d and oxygen 2p orbitals. The
spatial extend of our 3d Wannier orbitals (orthonormalized Nth order muffin-tin
orbitals) is close to that found for atomic Hartree-Fock orbitals. We define
Ligand orbitals as those linear combinations of the O 2p Wannier orbitals which
couple to the 3d orbitals for the chosen cluster. The use of ligand orbitals
allows for a minimal Hilbert space in multiplet ligand-field theory
calculations, thus reducing the computational costs substantially. The result
is a fast and simple ab initio theory, which can provide useful information
about local properties of correlated insulators. We compare results for NiO,
MnO and SrTiO3 with x-ray absorption, inelastic x-ray scattering, and
photoemission experiments. The multiplet ligand field theory parameters found
by our ab initio method agree within ~10% to known experimental values
Investigating 16O with the 15N(p,{\alpha})12C reaction
The 16O nucleus was investigated through the 15N(p,{\alpha})12C reaction at
excitation energies from Ex = 12 231 to 15 700 keV using proton beams from a 5
MeV Van de Graaff accelerator at beam energies of Ep = 331 to 3800 keV. Alpha
decay from resonant states in 16O was strongly observed for ten known excited
states in this region. The candidate 4-alpha cluster state at Ex = 15.1 MeV was
investigated particularly intensely in order to understand its particle decay
channels.Comment: Submitted for Proceedings of Fourth International Workshop on State
of the Art in Nuclear Cluster Physics (SOTANCP4), held from May 13 - 18, 2018
in Galveston, TX, US
The Structure of Barium in the hcp Phase Under High Pressure
Recent experimental results on two hcp phases of barium under high pressure
show interesting variation of the lattice parameters. They are here interpreted
in terms of electronic structure calculation by using the LMTO method and
generalized pseudopotential theory (GPT) with a NFE-TBB approach. In phase II
the dramatic drop in c/a is an instability analogous to that in the group II
metals but with the transfer of s to d electrons playing a crucial role in Ba.
Meanwhile in phase V, the instability decrease a lot due to the core repulsion
at very high pressure. PACS numbers: 62.50+p, 61.66Bi, 71.15.Ap, 71.15Hx,
71.15LaComment: 29 pages, 8 figure
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