167 research outputs found
One-dimensional Si chains embedded in Pt(111)and protected by a hexagonal boron-nitride monolayer
Using scanning tunneling microscopy, we show that Si deposition on Pt(111) at
300K leads to a network of one-dimensional Si chains. On the bare Pt(111)
surface, the chains, embedded into the Pt surface, are orientated along the
-direction. They disappear within a few hours in ultrahigh vacuum due to
the presence of residual gas. Exposing the chains to different gases
deliberately reveals that CO is largely responsible for the disappearance of
the chains. The chains can be stabilized by a monolayer of hexagonal boron
nitride, which is deposited prior to the Si deposition. The resulting Si chains
are rotated by 30{\deg} with respect to the chains on the bare Pt(111) surface
and survive even an exposure to air for 10 minutes.Comment: 8 pages, 4 Figure
Chemical versus van der Waals Interaction: The Role of the Heteroatom in the Flat Absorption of Aromatic Molecules C6H6, C5NH5, and C4N2H4 on the Cu(110) Surface
We perform first-principles calculations aimed at investigating the role of a heteroatom such as N in the chemical and long-range van der Waals (vdW) interactions for a flat adsorption of several-conjugated molecules on the Cu(110) surface. Our study reveals that the alignment of the molecular orbitals at the adsorbate-substrate interface depends on the number of heteroatoms. As a direct consequence, the molecule-surface vdW interactions involve not only pi-like orbitals which are perpendicular to the molecular plane but also sigma-like orbitals delocalized in the molecular plane
Graphene on the Ir(111) surface: from van der Waals to strong bonding
We calculated the properties of a graphene monolayer on the Ir(111) surface, using the model in which the periodicities of the two structures are assumed equal, instead of the observed slight mismatch which leads to a large superperiodic unit cell. We used the density functional theory approach supplemented with the recently developed van der Waals-density function (vdW-DF) non-local correlation functional. The latter is essential for treating the vdW interaction, which is crucial for the adsorption distances and energies of the rather weakly bound graphene. When additional iridium atoms are put on top of graphene, the electronic structure of C atoms acquires the sp(3) character and strong bonds with the iridium atoms are formed. We discuss the validity of the approximations used and their relevance to other graphene-metal systems
Real-space electronic-structure calculations with full-potential all-electron precision for transition-metals
We have developed an efficient computational scheme utilizing the real-space
finite-difference formalism and the projector augmented-wave (PAW) method to
perform precise first-principles electronic-structure simulations based on the
density functional theory for systems containing transition metals with a
modest computational effort. By combining the advantages of the time-saving
double-grid technique and the Fourier filtering procedure for the projectors of
pseudopotentials, we can overcome the egg box effect in the computations even
for first-row elements and transition metals, which is a problem of the
real-space finite-difference formalism. In order to demonstrate the potential
power in terms of precision and applicability of the present scheme, we have
carried out simulations to examine several bulk properties and structural
energy differences between different bulk phases of transition metals, and have
obtained excellent agreement with the results of other precise first-principles
methods such as a plane wave based PAW method and an all-electron
full-potential linearized augmented plane wave (FLAPW) method.Comment: 29 Page
Hybridisation at the organic-metal interface: a surface-scientific analogue of H\"uckel's rule?
We demonstrate that cyclooctatetraene (COT) can be stabilised in different
conformations when adsorbed on different noble-metal surfaces due to varying
molecule-substrate interaction. While at first glance the behaviour seems to be
in accordance with H\"uckel's rule, a theoretical analysis reveals no
significant charge transfer. The driving mechanism for the conformational
change is hybridisation at the organic-metal interface and does not necessitate
any charge transfer.Comment: Accepted for publication in Chemical Communications. Main article: 6
pages, 2 figures; Supplementary Information: 4 pages, 3 figures, 1 table. All
in one fil
Spin- and energy-dependent tunneling through a single molecule with intramolecular spatial resolution
We investigate the spin- and energy dependent tunneling through a single
organic molecule (CoPc) adsorbed on a ferromagnetic Fe thin film, spatially
resolved by low-temperature spin-polarized scanning tunneling microscopy.
Interestingly, the metal ion as well as the organic ligand show a significant
spin-dependence of tunneling current flow. State-of-the-art ab initio
calculations including also van-der-Waals interactions reveal a strong
hybridization of molecular orbitals and surface 3d states. The molecule is
anionic due to a transfer of one electron, resulting in a non-magnetic (S= 0)
state. Nevertheless, tunneling through the molecule exhibits a pronounced
spin-dependence due to spin-split molecule-surface hybrid states.Comment: Version of Submission, 18-03-201
Controlling the Local Spin-Polarization at the Organic-Ferromagnetic Interface
By means of ab initio calculations and spin-polarized scanning tunneling
microscopy experiments we show how to manipulate the local spin-polarization of
a ferromagnetic surface by creating a complex energy dependent magnetic
structure. We demonstrate this novel effect by adsorbing organic molecules
containing pi(pz)-electrons onto a ferromagnetic surface, in which the
hybridization of the out-of-plane pz atomic type orbitals with the d-states of
the metal leads to the inversion of the spin-polarization at the organic site
due to a pz - d Zener exchange type mechanism. As a key result, we demonstrate
that it is possible to selectively inject spin-up and spin-down electrons from
the same ferromagnetic surface, an effect which can be exploited in future
spintronic devices
DFT with nonlocal correlation: A key to the solution of the CO adsorption puzzle
We study the chemisorption of CO molecule into sites of different coordination on (111) surfaces of late 4d and 5d transition metals. In an attempt to solve the well-known CO adsorption puzzle, i.e. discrepancies of adsorption site preferences with experiment which appear in the standard Density Functional Theory calculations, we have applied the relatively new vdW-DF functional of nonlocal correlation. In all considered cases this reduces or completely solves the site preference discrepancies and improves the value of the adsorption energy. By introducing a cutoff distance for nonlocal interaction we can pinpoint the length scale at which the correlation plays a major role in the systems considered
JuNoLo - Jülich nonlocal code for parallel post-processing evaluation of vdW-DF correlation energy
Nowadays the state of the art Density Functional Theory (DFT) codes are based on local (LDA) or semilocal (GGA) energy functionals. Recently the theory of a truly nonlocal energy functional has been developed. It has been used mostly as a post-DFT calculation approach. i.e. by applying the functional to the charge density calculated using any standard DFT code, thus obtaining a new improved value for the total energy of the system. Nonlocal calculation is computationally quite expensive and scales as N-2 where N is the number of points in which the density is defined, and a massively parallel calculation is welcome for a wider applicability of the new approach. In this article we present a code which accomplishes this goal
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