212 research outputs found
First-principles calculation of Li adatom structures on the Mo(112) surface
The formation and structure of the ordered phases of Li atoms adsorbed on the Mo(112) surface are investigated by performing first-principles density-functional calculations. Large inward relaxation for the first atomic interlayer distance of the clean Mo(112) surface is found. The vertical relaxations of the substrate are only little influenced by the adsorbed Li atoms. The magnitude of lateral shifts of atoms along the atomic rows is found to be small and in line with measured values. The energetics of chain structures of Li adatoms for coverages 0.125<~Θ<~1 monolayer is determined and the p(4×1) and p(2×1) adatom structures are found to be the most favored ones in agreement with experiment. The binding energy of Li atoms decreases with increasing coverage. The calculated work function changes with Li adatom coverage are in good agreement with experiment. The energy barriers for adatom diffusion are determined and the energetics of lateral interactions between adatoms is discussed.Peer reviewe
To what extent could acute general psychiatric day care reduce inpatient admissions?
The multi-site research project (Acronym: EDEN-study) “Psychiatric day hospital treatment: An alternative to inpatient treatment, being cost-effective and minimizing post-treatment needs for care? An evaluative study in European countries with different care systems” was funded by the European Commission (Quality of Life and Management of Living, contract no. QLG4-CT-2000-01700). Additional national grants supporting the project were provided by Roland-Ernst-Stiftung für Gesundheitswesen and the Faculty of Medicine at the Dresden University of Technology, the National Health Service Executive Organization and Management Programme, the Polish National Committee of Scientific Affairs, and the Slovak Ministry of Education. Pfizer Pharmaceutical Company supported travel and accommodation for EDEN project meetings
Energetics of Sr adatom interactions on the Mo(112) surface
First-principles methods are used to investigate the formation and structure of the ordered phases of Sr atoms adsorbed on the furrowed Mo(112) surface. The energetics of various commensurate and incommensurate adatom structures providing information on lateral interactions between adatoms is determined for coverages 0.11⩽Θ⩽1 monolayer. It is found that the binding energy of Sr atoms decreases with increasing coverage. The experimentally observed p(8×1) and p(5×1) adatom chains are found to belong to the most favored structures for Θ<0.5. The energetic difference between these two structures amounts to 20meV. The experimental work function variation with Sr adatom coverage is very well reproduced. The energy barriers for Sr diffusion along the atomic troughs are calculated and discussed.Peer reviewe
Energetics of metal slabs and clusters: the rectangle-box model
An expansion of energy characteristics of wide thin slab of thickness L in
power of 1/L is constructed using the free-electron approximation and the model
of a potential well of finite depth. Accuracy of results in each order of the
expansion is analyzed. Size dependences of the work function and electronic
elastic force for Au and Na slabs are calculated. It is concluded that the work
function of low-dimensional metal structure is always smaller that of
semi-infinite metal sample.
A mechanism for the Coulomb instability of charged metal clusters, different
from Rayleigh's one, is discussed. The two-component model of a metallic
cluster yields the different critical sizes depending on a kind of charging
particles (electrons or ions). For the cuboid clusters, the electronic spectrum
quantization is taken into account. The calculated critical sizes of
Ag_{N}^{2-} and Au_{N}^{3-} clusters are in a good agreement with experimental
data. A qualitative explanation is suggested for the Coulomb explosion of
positively charged Na_{\N}^{n+} clusters at 3<n<5.Comment: 11 pages, 6 figures, 1 tabl
Potential Energy Surfaces for H Adsorbed at 4H-SiC{0001} Surfaces
The constant adsorption energy surfaces for hydrogen adsorbed on Si-and C-terminated hexagonal 4H-SiC{0001} surfaces have been calculated within density functional theory framework. The two unreconstructed and one reconstructed √ 3 × √ 3 surfaces were taken into account. We show that on all surfaces there is a global energy minimum indicating the most favourable adsorption site corresponding to H atom adsorption on-top of the topmost substrate layer atom. In case of reconstructed surface, there is another small and shallow local minimum. Moreover, the diusion barrier is much higher at reconstructed surface than at unreconstructed ones
Cohesive and magnetic properties of grain boundaries in bcc Fe with Cr additions
Structural, cohesive, and magnetic properties of two symmetric
and tilt grain boundaries (GBs) in pure bcc Fe and in dilute
FeCr alloys are studied from first principles. Different concentration and
position of Cr solute atoms are considered. We found that Cr atoms placed in
the GB interstice enhance the cohesion by 0.5-1.2 J/m. Substitutional Cr in
the layers adjacent to the boundary shows anisotropic effect on the GB
cohesion: it is neutral when placed in the (111) oriented Fe grains, and
enhances cohesion (by 0.5 J/m) when substituted in the boundary layer of
the (210) grains. The strengthening effect of the Cr solute is dominated by the
chemical component of the adhesive binding energy. Our calculations show that
unlike the free iron surfaces, Cr impurities segregate to the boundaries of the
Fe grains. The magnetic moments on GB atoms are substantially changed and their
variation correlates with the corresponding relaxation pattern of the GB
planes. The moments on Cr additions are 2-4 times enhanced in comparison with
that in a Cr crystal and are antiparallel to the moments on the Fe atoms
Optical conductivity of metal nanofilms and nanowires: The rectangular-box model
The conductivity tensor is introduced for the low-dimensional electron
systems. Within the particle-in-a-box model and the diagonal response
approximation, components of the conductivity tensor for a quasi-homogeneous
ultrathin metal film and wire are calculated under the assumption (where is the characteristic small dimension of the
system, is the Fermi wavelength for bulk metal). We find the
transmittance of ultrathin films and compare these results with available
experimental data. The analytical estimations for the size dependence of the
Fermi level are presented, and the oscillations of the Fermi energy in
ultrathin films and wires are computed. Our results demonstrate the strong size
and frequency dependences of the real and imaginary parts of the conductivity
components in the infrared range. A sharp distinction of the results for Au and
Pb is observed and explained by the difference in the relaxation time of these
metals.Comment: 13 pages, 8 figure
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