48,461 research outputs found
Spin Polarized Transport Through a Single-Molecule Magnet: Current-Induced Magnetic Switching
Magnetic switching of a single-molecule magnet (SMM) due to spin-polarized
current is investigated theoretically. The charge transfer between the
electrodes takes place via the lowest unoccupied molecular orbital (LUMO) of
the SMM. Generally, the double occupancy of the LUMO level, and a finite
on-site Coulomb repulsion, is taken into account. Owing to the exchange
interaction between electrons in the LUMO level and the SMM's spin, the latter
can be reversed. The perturbation approach (Fermi golden rule) is applied to
calculate current-voltage characteristics. The influence of Coulomb
interactions on the switching process is also analyzed.Comment: 5 pages with 4 EPS figures; version as accepted for publication in
Phys. Rev. B (more general model introduced
Laser-induced spin protection and switching in a specially designed magnetic dot: A theoretical investigation
Most laser-induced femtosecond magnetism investigations are done in magnetic
thin films. Nanostructured magnetic dots, with their reduced dimensionality,
present new opportunities for spin manipulation. Here we predict that if a
magnetic dot has a dipole-forbidden transition between the lowest occupied
molecular orbital (LUMO) and the highest unoccupied molecular orbital (HOMO),
but a dipole-allowed transition between LUMO+1 and HOMO, electromagnetically
inducedtransparency can be used to prevent ultrafast laser-induced spin
momentum reduction, or spin protection. This is realized through a strong dump
pulse to funnel the population into LUMO+1. If the time delay between the pump
and dump pulses is longer than 60 fs, a population inversion starts and spin
switching is achieved. Thesepredictions are detectable experimentally.Comment: 6 pages, three figur
Ab initio calculations of structural and electronic properties of CdTe clusters
We present results of a study of small stoichiometric
() clusters and few medium sized non-stoichiometric
[(); ()] clusters using the Density
Functional formalism and projector augmented wave method within the generalized
gradient approximation. Structural properties
{\it viz.} geometry, bond length, symmetry and electronic properties like
HOMO-LUMO gap, binding energy, ionization potential and nature of bonding {\it
etc.} have been analyzed. Medium sized non-stoichiometric clusters were
considered as fragments of the bulk with T{} symmetry. It was observed
that upon relaxation, the symmetry changes for the Cd rich clusters whereas the
Te rich clusters retain their symmetry. The Cd rich clusters develop a
HOMO-LUMO gap due to relaxation whereas there is no change in the HOMO-LUMO gap
of the Te rich clusters. Thus, the symmetry of a cluster seems to be an
important factor in determining the HOMO-LUMO gap.Comment: 8 pages 16 figure
Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level
We compare the charge transport characteristics of heavy doped p- and
n-Si-alkyl chain/Hg junctions. Photoelectron spectroscopy (UPS, IPES and XPS)
results for the molecule-Si band alignment at equilibrium show the Fermi level
to LUMO energy difference to be much smaller than the corresponding Fermi level
to HOMO one. This result supports the conclusion we reach, based on negative
differential resistance in an analogous semiconductor-inorganic insulator/metal
junction, that for both p- and n-type junctions the energy difference between
the Fermi level and LUMO, i.e., electron tunneling, controls charge transport.
The Fermi level-LUMO energy difference, experimentally determined by IPES,
agrees with the non-resonant tunneling barrier height deduced from the
exponential length-attenuation of the current
M\"obius and twisted graphene nanoribbons: stability, geometry and electronic properties
Results of classical force field geometry optimizations for twisted graphene
nanoribbons with a number of twists varying from 0 to 7 (the case =1
corresponds to a half-twist M\"obius nanoribbon) are presented in this work.
Their structural stability was investigated using the Brenner reactive force
field. The best classical molecular geometries were used as input for
semiempirical calculations, from which the electronic properties (energy
levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions
were also calculated in the complete active space framework taking into account
eigenstates from HOMO-4 to LUMO+4, as well as the oscillator strengths
corresponding to the first optical transitions in the UV-VIS range. The lowest
energy molecules were found less symmetric than initial configurations, and the
HOMO-LUMO energy gaps are larger than the value found for the nanographene used
to build them due to electronic localization effects created by the twisting. A
high number of twists leads to a sharp increase of the HOMO LUMO
transition energy. We suggest that some twisted nanoribbons could form crystals
stabilized by dipolar interactions
Resonant Lifetime of Core-Excited Organic Adsorbates from First Principles
We investigate by first-principles simulations the resonant electron-transfer
lifetime from the excited state of an organic adsorbate to a semiconductor
surface, namely isonicotinic acid on rutile TiO(110). The
molecule-substrate interaction is described using density functional theory,
while the effect of a truly semi-infinite substrate is taken into account by
Green's function techniques. Excitonic effects due to the presence of
core-excited atoms in the molecule are shown to be instrumental to understand
the electron-transfer times measured using the so-called core-hole-clock
technique. In particular, for the isonicotinic acid on TiO(110), we find
that the charge injection from the LUMO is quenched since this state lies
within the substrate band gap. We compute the resonant charge-transfer times
from LUMO+1 and LUMO+2, and systematically investigate the dependence of the
elastic lifetimes of these states on the alignment among adsorbate and
substrate states.Comment: 24 pages, 6 figures, to appear in Journal of Physical Chemistry
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