Implementing the Keldysh formalism into<i>ab initio</i>methods for the calculation of quantum transport: Application to metallic nanocontacts

Louis, E.; Vergés, J. A.; Palacios, J. J.; Pérez-Jiménez, Ángel J.; San‐Fabián, Emilio

doi:10.1103/physrevb.67.155321

Cited by 79 publications

(73 citation statements)

References 16 publications

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“…[19]. It is noted that the two results are remarkably similar, as expected whenever the bias voltage is not very large [20]. This supports the validity of the comparison of the transmission T (E) with the experimental results associating the external applied field to the variable E. In figure 2 we note that, increasing the density of states, the Fano antiresonance becomes wider and dipper and shifts to higher voltages.…”

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confidence: 82%

Kondo effect in transport through molecules adsorbed on metal surfaces: From Fano dips to Kondo peaks

et al. 2007

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The Kondo effect observed in recent STM experiments on transport through CoPc and TBrPP-Co molecules adsorbed on Au(111) and Cu(111) surfaces, respectively, is discussed within the framework of a simple model (Phys. Rev. Lett. 97, 076806 (2006)). It is shown that, in the Kondo regime and by varying the adequate model parameters, it is possible to produce a crossover from a conductance Kondo peak (CoPc) to a conductance Fano dip (TBrPP-Co). In the case of TBrPP-Co/Cu (111) we show that the model reproduces the changes in the shape of the Fano dip, the raising of the Kondo temperature and shifting to higher energies of the dip minimum when the number of nearest neighbors molecules is lowered. These features are in line with experimental observations indicating that our simple model contains the essential physics underlying the transport properties of such complex molecules. [2,3] in transport through a Co atom adsorbed on an Au(111) surface, a great deal of attention has been devoted to investigate, both theoretical and experimentally, such effect in either isolated Co atoms [4,5] or in Co-containing molecules [6,7,8,9] adsorbed on metal surfaces. The possibility of tuning the Kondo temperature [6,9] has been recently demonstrated, increasing considerably the interest of these systems. In particular it has been shown that, the characteristics, and even the existence, of the Kondo resonance can be controlled by distorting a CoPc molecule adsorbed on a Au(111) surface [6]. More recently [9] the Kondo temperature in a TBrPP-Co molecule adsorbed on a Cu(111) surface has been increased by decreasing the number of nearestneighbor TBrPP-Co molecules. The authors of [9] argued that this is due to a reduction of surfaces states when the number of nearest neighbors molecules around a given one is increased.One of the most interesting aspects of those two works is that while in the case of CoPc/Au(111) a Kondo peak was observed, in the experiments on TBrPP-Co/Cu(111) the conductance showed a Fano dip, as in isolated Co atoms adsorbed on metal surfaces [1,4,5]. Those two molecules, although largely different, have two outstanding similarities: i) both have the Co atom in the their geometric centers, and, ii) their STM images show four clearly defined lobes [6]. The enormous complexity of the electronic structure of these molecules and the manybody physics involved hinder a detailed account of these systems. One of the main goals of the present work is to show, using a simple model that catches the most prominent features of both molecules, under which circumstances dips or peaks appear in the transmission.A model Hamiltonian was taken assuming the following small atomic arrangement [8]: a central site with a single atomic orbital, a strong Coulomb repulsion at the Co atom and four lobes of the molecule described by four atomic orbitals placed on a square, which center is the Co atom (see Fig. 1 of Ref.[8]). Two additional orbitals located above and below the Co atom are included to represent the apex of the STM tip and an at...

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Kondo effect in transport through molecules adsorbed on metal surfaces: From Fano dips to Kondo peaks

et al. 2007

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“…Contour integration and sparse matrix techniques, together with parallelization over both k points and real space is exploited for optimal efficiency. Although the basic elements of our implementation are not new and have been described in earlier papers, [27][28][29][30] the possibility of applying a general gate and/or finite bias voltage, the use of multiple leads, and inclusion of nonequilibrium forces on the ions provides a flexible and efficient computational platform for general purpose modeling of charge transport at the nanoscale and should be of interest to a large and growing community. This paper is organized as follows.…”

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confidence: 99%

Ab initiononequilibrium quantum transport and forces with the real-space projector augmented wave method

2012

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We present an efficient implemention of a non-equilibrium Green function (NEGF) method for selfconsistent calculations of electron transport and forces in nanostructured materials. The electronic structure is described at the level of density functional theory (DFT) using the projector augmented wave method (PAW) to describe the ionic cores and an atomic orbital basis set for the valence electrons. External bias and gate voltages are treated in a self-consistent manner and the Poisson equation with appropriate boundary conditions is solved in real space. Contour integration of the Green function and parallelization over k-points and real space makes the code highly efficient and applicable to systems containing several hundreds of atoms. The method is applied to a number of different systems demonstrating the effects of bias and gate voltages, multiterminal setups, nonequilibrium forces, and spin transport.

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“…The results depicted in Fig. 2 are addressed to identify the origin of the emergence of the Kondo resonance upon distortion of the molecule [18,19,20]. The Figure shows results for either the Co atom ( Fig.…”

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Kondo Effect of an Adsorbed Cobalt Phthalocyanine (CoPc) Molecule: The Role of Quantum Interference

Chiappe

Louis

2006

Phys. Rev. Lett.

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A recent experimental study showed that, distorting a CoPc molecule adsorbed on a Au(111) surface, a Kondo effect is induced with a temperature higher than 200 K. We examine a model in which an atom with strong Coulomb repulsion (Co) is surrounded by four atoms on a square (molecule lobes), and two atoms above and below it representing the apex of the STM tip and an atom on the gold surface (all with a single, half-filled, atomic orbital). The Hamiltonian is solved exactly for the isolated cluster, and, after connecting the leads (STM tip and gold), the conductance is calculated by standard techniques. Quantum interference prevents the existence of the Kondo effect when the orbitals on the square do not interact (undistorted molecule); the Kondo resonance shows up after switching on that interaction. The weight of the Kondo resonance is controlled by the interplay of couplings to the STM tip and the gold surface, and between the molecule lobes. Coupling of localized spins to conduction electrons may lead to a transport anomaly known as the Kondo effect [1,2]. This effect, that usually shows up at low temperatures, consists of a sharp peak at the Fermi level, whose half-width is known as the Kondo temperature (T K ), and a conductance close to one conductance quantum G 0 = 2e 2 /h. The Kondo temperature in the case of magnetic impurities in non-magnetic metals is around 50 K [1], whereas in artificial atoms (quantum dots) is just a few hundred mK [3,4]. In a recent experiment [5,6] it has been shown that it is possible to control the characteristics, and even the existence, of the Kondo resonance by modifying the chemical surroundings of a magnetic atom. The experiments were carried out on a cobalt phthalocyanine molecule (CoPc) adsorbed on a Au(111) surface. Dehydrogenation of this molecule (d-CoPc) by means of voltage pulses from a Scanning Tunneling Microscope (STM) triggered a Kondo effect with a rather high Kondo temperature (T K ≈ 200 K). This temperature is even higher than that observed for bare Co adsorbed on a similar surface [6,7]. Besides such a high T K , one of the most remarkable results of [5] is the fact that the undistorted molecule does not show a Kondo effect, while it is readily promoted by distorting the molecule upon dehydrogenation. Topographic images taken by means of the STM [5] indicated that the CoPc molecule has four almost non-overlapping lobes symmetrically placed around the Co atom. Dehydrogenation distorts the molecule and forces those lobes to overlap. In addition it strongly decreases the distance from the molecule lobes to the gold surface and increases the Co/gold surface distance in approximately 30% [5].We hereby propose a simple model that accounts for some of the salient features of the experiment described above. We take a model Hamiltonian on a small atomic arrangement which is solved exactly, and subsequently connected to semi-infinite chains used to describe the STM tip and the gold surface. Fig. 1 depicts this atomic arrangement. A central site with a single atomic or...

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Implementing the Keldysh formalism intoab initiomethods for the calculation of quantum transport: Application to metallic nanocontacts

Cited by 79 publications

References 16 publications

Kondo effect in transport through molecules adsorbed on metal surfaces: From Fano dips to Kondo peaks

Kondo effect in transport through molecules adsorbed on metal surfaces: From Fano dips to Kondo peaks

Ab initiononequilibrium quantum transport and forces with the real-space projector augmented wave method

Kondo Effect of an Adsorbed Cobalt Phthalocyanine (CoPc) Molecule: The Role of Quantum Interference

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