Further developments in the local-orbital density-functional-theory tight-binding method

Lewis, James P.; Glaesemann, Kurt R.; Voth, Gregory A.; Fritsch, Jürgen; Demkov, Alexander A.; Ortega, José; Sankey, Otto F.

doi:10.1103/physrevb.64.195103

Cited by 244 publications

(171 citation statements)

References 58 publications

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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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van der Waals interactions mediating the cohesion of fullerenes on graphene

et al. 2012

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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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“…3 In this paper, we combine standard density functional theory ͑DFT͒ plane-wave ͑PW͒ pseudopotential methods for the accurate determination of the tip and sample structure and electronic properties, with a calculation of STM currents based on nonequilibrium Keldysh-Green function techniques. [4][5][6] The connection between the structural and transport calculations is done through a fast local-orbital DFT technique ͑Fireball2003͒, 7,8 which efficiently maps the electronic Hamiltonian determined from the PW calculation, and can be naturally linked with the transport formalism, which is expressed in terms of localized orbitals. 6 This approach incorporates the influence of the bias and current conditions as well as a realistic description of the tips chemical nature ͑either Pt or Ir͒ used in the experiments and their possible contamination.…”

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“…6, the connection between the structural and transport calculations is done through a fast local-orbital DFT technique ͑Fireball2003͒. 7,8 In Fireball, the valence wave functions for either O or the transition metal atoms are expanded in a set of strictly localized pseudoatomic orbitals. This offers a very favorable accuracy/efficiency balance if the atomic-like basis set is chosen carefully ͑see Refs.…”

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Origin of contrast in STM images of oxygen on Pd(111) and its dependence on tip structure and tunneling parameters

et al. 2005

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The dependence of the contrast and symmetry of scanning tunneling microscope images of O / Pd͑111͒ −2 ϫ 2 on the structure of the tunneling tip and on tunneling parameters is explained using first-principles density functional theory. Experimentally, the contrast changes in different ways when a metal-terminated tip over hcp and top sites changes its bias and tip-sample distance. These changes are also reflected in the symmetry of the image. A detailed analysis of the tunneling contributions indicates that for the metallic tips, the Pd d orbitals are determining the image symmetry at close range and low bias, while at larger separations and high bias the Pd p z orbitals are the ones that control the image contrast. For oxygen-terminated tips, we predict a positive image contrast, associated with the tip oxygen bonds, as opposed to the negative contrast images obtained with metallic tips.

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Further developments in the local-orbital density-functional-theory tight-binding method

Cited by 244 publications

References 58 publications

van der Waals interactions mediating the cohesion of fullerenes on graphene

van der Waals interactions mediating the cohesion of fullerenes on graphene

Conductance of a conjugated molecule with carbon nanotube contacts

Origin of contrast in STM images of oxygen on Pd(111) and its dependence on tip structure and tunneling parameters

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