43 research outputs found
Van der Waals contribution to the inelastic atom-surface scattering
A calculation of the inelastic scattering rate of Xe atoms on Cu(111) is
presented. We focus in the regimes of low and intermediate velocities, where
the energy loss is mainly associated to the excitation electron-hole pairs in
the substrate. We consider trajectories parallel to the surface and restrict
ourselves to the Van der Waals contribution. The decay rate is calculated
within a self-energy formulation. The effect of the response function of the
substrate is studied by comparing the results obtained with two different
approaches: the Specular Reflection Model and the Random Phase Approximation.
In the latter, the surface is described by a finite slab and the wave functions
are obtained from a one-dimensional model potential that describes the main
features of the surface electronic structure while correctly retains the
image-like asymptotic behaviour. We have also studied the influence of the
surface state on the calculation, finding that it represents around 50% of the
total probability of electron-hole pairs excitation.Comment: 7 pages, 4 figure
Ab initio study of the double row model of the Si(553)-Au reconstruction
Using x-ray diffraction Ghose et al. [Surf. Sci. {\bf 581} (2005) 199] have
recently produced a structural model for the quantum-wire surface Si(553)-Au.
This model presents two parallel gold wires located at the step edge. Thus, the
structure and the gold coverage are quite different from previous proposals. We
present here an ab initio study using density functional theory of the
stability, electronic band structure and scanning tunneling microscopy images
of this model.Comment: Submitted to Surface Science on December 200
Calculation of the optical response of C60 and Na8 using time-dependent density functional theory and local orbitals
We report on a general method for the calculation of the frequency-dependent
optical response of clusters based upon time-dependent density functional
theory (TDDFT). The implementation is done using explicit propagation in the
time domain and a self-consistent program that uses a linear combination of
atomic orbitals (LCAO). Our actual calculations employ the SIESTA program,
which is designed to be fast and accurate for large clusters. We use the
adiabatic local density approximation to account for exchange and correlation
effects. Results are presented for the imaginary part of the linear
polarizability, Im [\alpha(w)], and the dipole strength function, S(w), of C60
and Na8, compared to previous calculations and to experiment. We also show how
to calculate the integrated frequency-dependent second order non-linear
polarizability for the case of a step function electric field,
\gamma_{step}(w), and present results for C60.Comment: 11 pages with 6 postscript figures. Submitted for publicatio
Search for a Metallic Dangling-Bond Wire on -doped H-passivated Semiconductor Surfaces
We have theoretically investigated the electronic properties of neutral and
-doped dangling bond (DB) quasi-one-dimensional structures (lines) in the
Si(001):H and Ge(001):H substrates with the aim of identifying atomic-scale
interconnects exhibiting metallic conduction for use in on-surface circuitry.
Whether neutral or doped, DB lines are prone to suffer geometrical distortions
or have magnetic ground-states that render them semiconducting. However, from
our study we have identified one exception -- a dimer row fully stripped of
hydrogen passivation. Such a DB-dimer line shows an electronic band structure
which is remarkably insensitive to the doping level and, thus, it is possible
to manipulate the position of the Fermi level, moving it away from the gap.
Transport calculations demonstrate that the metallic conduction in the DB-dimer
line can survive thermally induced disorder, but is more sensitive to imperfect
patterning. In conclusion, the DB-dimer line shows remarkable stability to
doping and could serve as a one-dimensional metallic conductor on -doped
samples.Comment: 8 pages, 5 figure
Characterization of single-molecule pentanedithiol junctions by inelastic electron tunneling spectroscopy and first-principles calculations
We study pentanedithiol molecular junctions formed by means of the
break-junction technique with a scanning tunneling microscope at low
temperatures. Using inelastic electron tunneling spectroscopy and
first-principles calculations, the response of the junction to elastic
deformation is examined. We show that this procedure makes a detailed
characterization of the molecular junction possible. In particular, our results
indicate that tunneling takes place through just a single molecule.Comment: 5 pages, 4 figures (accepted in Phys. Rev. B