Multicenter approach to the exchange-correlation interactions in<i>ab initio</i>tight-binding methods

Jelı́nek, Pavel; Wang, Hao; Lewis, James P.; Sankey, Otto F.; Ortega, José

doi:10.1103/physrevb.71.235101

Cited by 250 publications

(237 citation statements)

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“…We have carried out simulations of the current between a W tip and a graphene bilayer. We map the first-principles Hamiltonian in a local orbital basis [34] and use a nonequilibrium Green's function formalism that includes the multiple scattering effects to all orders [8,32]. The critical importance of these effects in the evolution of the contrast can be clearly seen in the constant-height profiles (Fig.…”

Section: Prl 106 176101 (2011) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

Forces and Currents in Carbon Nanostructures: Are We Imaging Atoms?

et al. 2011

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First-principles calculations show that the rich variety of image patterns found in carbon nanostructures with the atomic force and scanning tunneling microscopes can be rationalized in terms of the chemical reactivity of the tip and the distance range explored in the experiments. For weakly reactive tips, the Pauli repulsion dominates the atomic contrast and force maxima are expected on low electronic density positions as the hollow site. With reactive tips, the interaction is strong enough to change locally the hybridization of the carbon atoms, making it possible to observe atomic resolution in both the attractive and the repulsive regime although with inverted contrast. Regarding STM images, we show that in the near-contact regime, due to current saturation, bright spots correspond to hollow positions instead of atomic sites, providing an explanation for the most common hexagonal pattern found in the experiments. Fullerenes, nanotubes, graphene, and carbon nanoribbons are among the most promising materials for nanotechnological applications due to their unique mechanical and electronic properties [1,2]. Turning these expectations into real-world devices requires tools like the STM and the atomic force microscope (AFM) with true atomic resolution (FM-AFM) [3] to visualize, characterize, and manipulate these materials at the atomic scale. However, in spite of the apparent simplicity of the common honeycomb structure and the long-standing experimental research effort, we do not know yet something as fundamental as whether the maxima in the scanning probe microscopy images correspond to atoms or to the hollow sites [4][5][6][7]. Here, we use first-principles calculations to show that the rich variety of AFM and STM image patterns found in carbon nanostructures can be rationalized in terms of the chemical reactivity of the tip and the distance range explored in the experiments.The first STM images of the graphite(0001) surface did not display the expected honeycomb pattern but a hexagonal arrangement of bright spots (topographic maxima; see Fig. 1 in [8]) [9][10][11]. The accepted interpretation relies on a subtle electronic effect [12]. The Bernal stacking makes the two surface atoms inequivalent. C atoms, with a nearest neighbor right below in the second layer, do not contribute significantly to the density of states close to the Fermi level, and only the C atoms are imaged as bright spots at low bias voltages. Although a honeycomb pattern should be recovered for larger biases, the experimental evidence accumulated over the past 25 years [9][10][11][12][13] shows that STM images with a hexagonal pattern are overwhelmingly recorded over a broad range of bias voltages and distance operation conditions. Nevertheless, several groups have reported honeycomb patterns even for small bias voltage [13][14][15][16][17].The FM-AFM, relying on the forces between the tip and surface, is expected not to be so sensitive to electronic effects and to reflect the real atomic structure of the surface. However, the first reported ...

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Section: Prl 106 176101 (2011) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

Forces and Currents in Carbon Nanostructures: Are We Imaging Atoms?

et al. 2011

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“…These two contributions are treated in perturbation theory from a DFT calculation using the FIREBALL code. 17,[30][31][32] This method takes into account particularly the π -π interactions since the corresponding overlaps are the dominant effect in this weakly interacting system. The underlying SiC buffer [33][34][35][36][37] layer was neglected, since the expected energy contribution to the C 60 total energy due to the vdW interaction is at least an order of magnitude lower than the contribution due to the presence of SLG, 18 considering the large separation of SLG and the buffer layer.…”

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van der Waals interactions mediating the cohesion of fullerenes on graphene

et al. 2012

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Fullerenes on single-layer epitaxial graphene are a model system to study very faint interactions at a molecular level. By a variable temperature scanning tunneling microscope we have been able to study ordered fullerene layers at 40 K, exclusively bound by van der Waals interactions. The experimentally determined adsorption geometry of the molecules is computationally confirmed only if van der Waals interactions are included in the calculation formalism. The relative orientation of fullerenes in their close-packed arrangement is found to be the crucial factor for determining the total energy. Observation of collective movements of fullerene islands points out the weak coupling to the substrate and the important role of the van der Waals cohesion forces within. Mechanical stability, friction, or adhesion are among the physical properties that strongly depend on van der Waals (vdW) interactions. This is also true for the nanoscale. The nucleation and growth of molecular surface structures involve dynamic processes such as diffusion, molecular rotations, or conformational changes, which rely also on vdW intermolecular interactions. 1,2 Moreover, self-assembly and adsorption studies focus on determining the preferred adsorption site and configuration, the adsorbate-adsorbate interaction, and the distance between the adsorbate and substrate (e.g., Ref. 3).There is an increasing interest in the role of vdW interactions of organic molecules on graphite and other surfaces. 4,5 Generally, long-distance forces as vdW are not described by the most widely used functionals of the density-functional theory (DFT). Thus, in many of the works performed until now they are simply not included. However, when planar systems of carbon-based materials are in question, they require a different approach to the interplay between intermolecular (lateral) and adsorbate-substrate (vertical) interactions in determining the properties of ordered molecular structures. To evidence the important role of the vdW interactions in adsorption processes we have chosen a system of a very weakly interacting substrate and adsorbate, single-layer graphene (SLG) 6 and fullerenes (C 60 ). 7 The fact that both materials consist exclusively of carbon atoms arranged in an atomically thin planar mesh without H or any other atoms inside the atomic structure that could lead to long-range H-bond interactions makes this system a good prototype for a demonstration of the effect of these forces at a molecular level.Thus, we consider the C 60 on SLG grown on 6H-SiC(0001) 8-10 as a model system to test the strength of the vdW forces and mutual interactions that occur between neutral inert nanostructures. C 60 adsorbed on surfaces generally tend to form hexagonal close-packed arrangements 11 in order to optimize their lateral interactions. In very recent studies of C 60 molecules deposited on SLG epitaxially grown on metal, 12,13 it has been shown that the interaction between the molecules and the substrate, and consequently the molecular arrangement, is ruled by the m...

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“…To calculate the equilibrium transmission of a CNT-molecule-CNT system, our method uses density functional theory (DFT) implemented by the ab initio tight-binding molecular dynamics code FIREBALL [24,25,26] coupled with a non-equilibrium Greeen's functional (NEGF) algorithm [21,27,28,29,30]. The BLYP exchange-correlation functional is used to perform a self-consistent calculation [31,32] using a double numeric sp 3 localized orbital FIREBALL basis.…”

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Conductance of a conjugated molecule with carbon nanotube contacts

et al. 2009

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Calculations of the conductance of a carbon nanotube (CNT)-molecule-CNT structure are in agreement with experimental measurements [1]. The features in the transmission correspond directly to the features of the isolated molecular orbitals. The HOMO provides conductance at low bias that is relatively insensitive to the end groups of the cut CNTs, the cut angle, or the number of molecular bridges. A molecular conformation change not directly in the path of the carrier transport increases the resistance by over 2 orders of magnitude.

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Multicenter approach to the exchange-correlation interactions inab initiotight-binding methods

Cited by 250 publications

References 40 publications

Forces and Currents in Carbon Nanostructures: Are We Imaging Atoms?

Forces and Currents in Carbon Nanostructures: Are We Imaging Atoms?

van der Waals interactions mediating the cohesion of fullerenes on graphene

Conductance of a conjugated molecule with carbon nanotube contacts

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