37 research outputs found
Surface effects on the electronic energy loss of charged particles entering a metal surface
Surface effects on the electronic energy loss of charged particles entering a
metal surface are investigated within linear-response theory, in the framework
of time-dependent density functional theory. Interesting phenomena occur in the
loss spectra originated by the boundary (bregenzung) effect, which is as a
consequence of the orthogonality of surface and bulk excitation modes. Our
calculations indicate that the presence of a non-abrupt electron-density
profile at the surface severely affects the nature of surface excitations, as
deduced from comparison with simplified models.Comment: 7 pages, 3 figures, to appear in J. Electron Spectros
Atom Transfer and Single-Adatom Contacts
The point contact of a tunnel tip approaching towards Ag(111) and Cu(111)
surfaces is investigated with a low temperature scanning tunneling microscope.
A sharp jump-to-contact, random in nature, is observed in the conductance.
After point contact, the tip-apex atom is transferred to the surface,
indicating that a one-atom contact is formed during the approach. In sharp
contrast, the conductance over single silver and copper adatoms exhibits a
smooth and reproducible transition from tunneling to contact regime. Numerical
simulations show that this is a consequence of the additional dipolar bonding
between the homoepitaxial adatom and the surface atoms.Comment: 4 pages, 4 figure
High-Level Correlated Approach to the Jellium Surface Energy, Without Uniform-Electron-Gas Input
We resolve the long-standing controversy over the surface energy of simple
metals: Density functional methods that require uniform-electron-gas input
agree with each other at many levels of sophistication, but not with high-level
correlated calculations like Fermi Hypernetted Chain and Diffusion Monte Carlo
(DMC) that predict the uniform-gas correlation energy. Here we apply a very
high-level correlated approach, the inhomogeneous Singwi-Tosi-Land-Sj\"olander
(ISTLS) method, and find that the density functionals are indeed reliable
(because the surface energy is "bulk-like"). ISTLS values are close to
recently-revised DMC values. Our work also vindicates the previously-disputed
use of uniform-gas-based nonlocal kernels in time-dependent density functional
theory.Comment: 4 pages, 1 figur
The role of surface elasticity in giant corrugations observed by scanning tunneling microscopes
Due to the importance of scanning tunneling microscopy for atomic scale research the anomalously high corrugation values on close packed metal surfaces have been the subject of debate and extensive theoretical work in the past two decades. To date it remained unclear, how surface properties and electronic structures are related to forces and interactions. Here we show that elasticity, in particular the high elasticity of aluminum surfaces, enhances corrugation by up to one order of magnitude. The parameter-free simulations yield correct results for all close packed metal surfaces and emphasize the importance of atomic relaxations for chemisorption processes. (C) 2004 Elsevier B.V. All rights reserved