556 research outputs found
Determination of Compton profiles at solid surfaces from first-principles calculations
Projected momentum distributions of electrons, i.e. Compton profiles above
the topmost atomic layer have recently become experimentally accessible by
kinetic electron emission in grazing-incidence scattering of atoms at
atomically flat single crystal metal surfaces. Sub-threshold emission by slow
projectiles was shown to be sensitive to high-momentum components of the local
Compton profile near the surface. We present a method to extract momentum
distribution, Compton profiles, and Wigner and Husimi phase space distributions
from ab-initio density-functional calculations of electronic structure. An
application for such distributions to scattering experiments is discussed.Comment: 13 pages, 5 figures, submitted to PR
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
Representation of Lipschitz Maps and Metric Coordinate Systems
[EN] Here, we prove some general results that allow us to ensure that specific representations (as well as extensions) of certain Lipschitz operators exist, provided we have some additional information about the underlying space, in the context of what we call enriched metric spaces. In this conceptual framework, we introduce some new classes of Lipschitz operators whose definition depends on the notion of metric coordinate system, which are defined by specific dominance inequalities involving summations of distances between certain points in the space. We analyze ÂżPietsch Theorem inspired factorizations" through subspaces of `Âż and L1, which are proved to characterize when a given metric space is Lipschitz isomorphic to a metric subspace of these spaces. As an application, extension results for Lipschitz maps that are obtained by a coordinate-wise adaptation of the McShaneÂżWhitney formulas, are also given.The first author was supported by a contract of the Programa de Ayudas de Investigacion y Desarrollo (PAID-01-21), Universitat Politecnica de Valencia. The third author was supported by Grant PID2020-112759GB-I00 funded by MCIN/AEI/10.13039/501100011033.Arnau-Notari, AR.; Calabuig, JM.; SĂĄnchez PĂ©rez, EA. (2022). Representation of Lipschitz Maps and Metric Coordinate Systems. Mathematics. 10(20):1-23. https://doi.org/10.3390/math10203867123102
Modeling Ferro- and Antiferromagnetic Interactions in Metal-Organic Coordination Networks
Magnetization curves of two rectangular metal-organic coordination networks
formed by the organic ligand TCNQ (7,7,8,8-tetracyanoquinodimethane) and two
different (Mn and Ni) 3d transition metal atoms [M(3d)] show marked differences
that are explained using first principles density functional theory and model
calculations. We find that the existence of a weakly dispersive hybrid band
with M(3d) and TCNQ character crossing the Fermi level is determinant for the
appearance of ferromagnetic coupling between metal centers, as it is the case
of the metallic system Ni-TCNQ but not of the insulating system Mn-TCNQ. The
spin magnetic moment localized at the Ni atoms induces a significant spin
polarization in the organic molecule; the corresponding spin density being
delocalized along the whole system. The exchange interaction between localized
spins at Ni centers and the itinerant spin density is ferromagnetic. Based on
two different model Hamiltonians, we estimate the strength of exchange
couplings between magnetic atoms for both Ni- and Mn-TCNQ networks that results
in weak ferromagnetic and very weak antiferromagnetic correlations for Ni- and
Mn-TCNQ networks, respectively.Comment: 27 pages, 6 figures, accepted for publication; Journal of Physical
Chemistry C (2014
Deployment feasibility studies of variable buoyancy anchors for floating wind applications
Postprin
Virtual Prototyping of a floating wind farm anchor during underwater towing operations
Postprin
The Role of the Magnetic Anisotropy in Atomic-Spin Sensing of 1D Molecular Chains
One-dimensional metal-organic chains often possess a complex magnetic
structure susceptible to be modified by a alteration of their chemical
composition. The possibility to tune their magnetic properties provides an
interesting playground to explore quasiparticle interactions in low-dimensional
systems. Despite the great effort invested so far, a detailed understanding of
the interactions governing the electronic and magnetic properties of the
low-dimensional systems is still incomplete. One of the reasons is the limited
ability to characterize their magnetic properties at the atomic scale. Here, we
provide a comprehensive study of the magnetic properties of metal-organic
one-dimensional (1D) coordination polymers consisting of
2,5-diamino-1,4-benzoquinonediimine ligands coordinated with Co or Cr atoms
synthesized in ultra-high vacuum conditions on a Au(111) surface. A combination
of an integral X-ray spectroscopy with local-probe inelastic electron tunneling
spectroscopy corroborated by multiplet analysis, density functional theory, and
inelastic electron tunneling simulations enable us to obtain essential
information about their magnetic structure, including the spin magnitude and
orientation at the magnetic atoms, as well as the magnetic anisotropy.Comment: 35 pages, 8 Figures, 3 table
Bipolar conductance switching of single anthradithiophene molecules
The authors acknowledge funding by the Emmy-Noether-Program of the Deutsche Forschungsgemeinschaft, the SFB 767, and the Baden-WĂŒrttemberg Stiftung. R.P. and A.A. thank the Basque Departamento de Universidades e Investigacion (grant no. IT-756-13) and the Spanish Ministerio de Economia y Competitividad (grant no. FIS2013-48286-C2-8752-P) for financial support.Single molecular switches are basic device elements in organic electronics. The pentacene analogue anthradithiophene (ADT) shows a fully reversible binary switching between different adsorption conformations on a metallic surface accompanied by a charge transfer. These transitions are activated locally in single molecules in a low-temperature scanning tunneling microscope . The switching induces changes between bistable orbital structures and energy level alignment at the interface. The most stable geometry, the âoffâ state, which all molecules adopt upon evaporation, corresponds to a short adsorption distance at which the electronic interactions of the acene rings bend the central part of the molecule toward the surface accompanied by a significant charge transfer from the metallic surface to the ADT molecules. This leads to a shift of the lowest unoccupied molecular orbital down to the Fermi level (EF). In the âonâ state the molecule has a flat geometry at a larger distance from the surface; consequently the interaction is weaker, resulting in a negligible charge transfer with an orbital structure resembling the highest occupied molecular orbital when imaged close to EF. The potential barrier between these two states can be overcome reversibly by injecting charge carriers locally into individual molecules. Voltage-controlled current traces show a hysteresis characteristic of a bipolar switching behavior. The interpretation is supported by first-principles calculations.PostprintPeer reviewe
Electric-field-driven direct desulfurization
The ability to elucidate the elementary steps of a chemical reaction at the atomic scale is important for the detailed understanding of the processes involved, which is key to uncover avenues for improved reaction paths. Here, we track the chemical pathway of an irreversible direct desulfurization reaction of tetracenothiophene adsorbed on the Cu(111) closed-packed surface at the submolecular level. Using the precise control of the tip position in a scanning tunneling microscope and the electric field applied across the tunnel junction, the two carbonâsulfur bonds of a thiophene unit are successively cleaved. Comparison of spatially mapped molecular states close to the Fermi level of the metallic substrate acquired at each reaction step with density functional theory calculations reveals the two elementary steps of this reaction mechanism. The first reaction step is activated by an electric field larger than 2 V nmâ1, practically in absence of tunneling electrons, opening the thiophene ring and leading to a transient intermediate. Subsequently, at the same threshold electric field and with simultaneous injection of electrons into the molecule, the exergonic detachment of the sulfur atom is triggered. Thus, a stable molecule with a bifurcated end is obtained, which is covalently bound to the metallic surface. The sulfur atom is expelled from the vicinity of the molecule.PostprintPeer reviewe
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