55 research outputs found
Electronic and structural properties of GaN by the full-potential LMTO method : the role of the electrons
The structural and electronic properties of cubic GaN are studied within the
local density approximation by the full-potential linear muffin-tin orbitals
method. The Ga electrons are treated as band states, and no shape
approximation is made to the potential and charge density. The influence of
electrons on the band structure, charge density, and bonding properties is
analyzed. It is found that due to the energy resonance of the Ga 3 states
with nitrogen 2 states, the cation bands are not inert, and features
unusual for a III-V compound are found in the lower part of the valence band
and in the valence charge density and density of states. To clarify the
influence of the Ga states on the cohesive properties, additional full and
frozen--overlapped-core calculations were performed for GaN, cubic ZnS, GaAs,
and Si. The results show, in addition to the known importance of non-linear
core-valence exchange-correlation corrections, that an explicit description of
closed-shell repulsion effects is necessary to obtain accurate results for GaN
and similar systems. In summary, GaN appears to be somewhat exceptional among
the III-V compounds and reminiscent of II-VI materials, in that its band
structure and cohesive properties are sensitive to a proper treatment of the
cation bands, as a result of the presence of the latter in the valence band
range.Comment: ( 20 REVTEX-preprint pages (REVTEX macros are included) 8 figures
available upon reques
Reconstruction Mechanism of FCC Transition-Metal (001) Surfaces
The reconstruction mechanism of (001) fcc transition metal surfaces is
investigated using a full-potential all-electron electronic structure method
within density-functional theory. Total-energy supercell calculations confirm
the experimental finding that a close-packed quasi-hexagonal overlayer
reconstruction is possible for the late 5-metals Ir, Pt, and Au, while it is
disfavoured in the isovalent 4 metals (Rh, Pd, Ag). The reconstructive
behaviour is driven by the tensile surface stress of the unreconstructed
surfaces; the stress is significantly larger in the 5 metals than in 4
ones, and only in the former case it overcomes the substrate resistance to the
required geometric rearrangement. It is shown that the surface stress for these
systems is due to charge depletion from the surface layer, and that the
cause of the 4th-to-5th row stress difference is the importance of relativistic
effects in the 5 series.Comment: RevTeX 3.0, 12 pages, 1 PostScript figure available upon request] 23
May 199
Magnetic tight-binding and the iron-chromium enthalpy anomaly
We describe a self consistent magnetic tight-binding theory based in an
expansion of the Hohenberg-Kohn density functional to second order, about a non
spin polarised reference density. We show how a first order expansion about a
density having a trial input magnetic moment leads to the Stoner--Slater rigid
band model. We employ a simple set of tight-binding parameters that accurately
describes electronic structure and energetics, and show these to be
transferable between first row transition metals and their alloys. We make a
number of calculations of the electronic structure of dilute Cr impurities in
Fe which we compare with results using the local spin density approximation.
The rigid band model provides a powerful means for interpreting complex
magnetic configurations in alloys; using this approach we are able to advance a
simple and readily understood explanation for the observed anomaly in the
enthalpy of mixing.Comment: Submitted to Phys Rev
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[no abstract available
Effects of the reduction of the number of cylinders of commercial engines on combustion and friction determined with a method of engine map scaling
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