419 research outputs found
Polaronic distortion and vacancy-induced magnetism in MgO
The electronic structure of the neutral and singly charged Mg vacancy in MgO
is investigated using density functional theory. For both defects, semilocal
exchange correlation functionals such as the local spin density approximation
incorrectly predict a delocalized degenerate ground state. In contrast
functionals that take strong correlation effects into account predict a
localized solution, in agreement with spin resonance experiments. Our results,
obtained with the HSE hybrid, atomic self-interaction corrected and LDA+U
functionals, provide a number of constraints to the possibility of
ferromagnetism in hole doped MgO
Influence of quantum confinement on the ferromagnetism of (Ga,Mn)As diluted magnetic semiconductor
We investigate the effect of quantum confinement on the ferromagnetism of
diluted magnetic semiconductor GaMnAs using a combination of
tight-binding and density functional methods. We observe strong majority-spin
Mn -As hybridization, as well as half metallic behavior, down to sizes
as small as 20 \AA in diameter. Below this critical size, the doped holes are
self-trapped by the Mn-sites, signalling both valence and electronic
transitions. Our results imply that magnetically doped III-V nanoparticles will
provide a medium for manipulating the electronic structure of dilute magnetic
semiconductors while conserving the ferromagnetic properties and even enhancing
it in certain size regime.Comment: 4 pages, 3 figure
Ab-initio transport theory for digital ferromagnetic heterostructures
MnAs/GaAs superlattices, made by -doping GaAs with Mn, are known as
digital ferromagnetic heterostructures. Here we present a theoretical density
functional study of the electronic, magnetic and transport properties of such
heterostructures. In the absence of intrinsic donors these systems show an half
metallic density of states, with an exchange interaction much stronger than
that of a random alloy with the same Mn concentration. {\it Ab initio}
ballistic transport calculations show that the carriers with energies close to
the Fermi energy are strongly confined within a few monolayers around the MnAs
plane. This strong confinement is responsible for the large exchange coupling.
Therefore the system can be described as a two dimensional half metal with
large conductance in the MnAs plane and small conductance in the perpendicular
direction
Ab initio study of electron transport in dry poly(G)-poly(C) A-DNA strands
The bias-dependent transport properties of short poly(G)-poly(C) A-DNA
strands attached to Au electrodes are investigated with first principles
electronic transport methods. By using the non- equilibrium Green's function
approach combined with self-interaction corrected density functional theory, we
calculate the fully self-consistent coherent I-V curve of various double-strand
polymeric DNA fragments. We show that electronic wave-function localization,
induced either by the native electrical dipole and/or by the electrostatic
disorder originating from the first few water solvation layers, drastically
suppresses the magnitude of the elastic conductance of A-DNA oligonucleotides.
We then argue that electron transport through DNA is the result of
sequence-specific short-range tunneling across a few bases combined with
general diffusive/inelastic processes.Comment: 15 pages, 13 figures, 1 tabl
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