Search

Electronic transport mechanisms in molecular junctions are investigated by a combination of first-principles calculations and current−voltage measurements of several well-characterized structures. We study self-assembled layers of alkanethiols grown on Au(111) and form tunnel junctions by contacting the molecular layers with the tip of a conductive force microscope. Measurements done under low-load conditions permit us to obtain reliable tilt-angle and molecular length dependencies of the low-bias conductance through the alkanethiol layers. The observed dependence on tilt-angle is stronger for the longer molecular chains. Our calculations confirm the observed trends and explain them as a result of two mechanisms, namely, a previously proposed intermolecular tunneling enhancement as well as a hitherto overlooked tilt-dependent molecular gate effect., T.F., D.S.P. and A.A. acknowledge support from Basque Departamento de Educación, UPV/EHU (Grant No. IT-366-07), the Spanish Ministerio de Ciencia e Innovación (Grants No. FIS2007-6671-C02-01, FIS2007-66711-C02-02 and MAT2007-62732), the ETORTEK program funded by the Basque Departamento de Industria and the Diputación Foral de Guipuzcoa, and the EC under contract No. NMP4-CT-2006-032109 (STREP “SURMOF”). T.F. acknowledges support from the Danish FNU (Grant No. 272-07-0114).

The effect of preadsorbed oxygen on the subsequent adsorption and reactions of water on Ru(0001) has been studied using low temperature scanning tunneling microscopy and DFT calculations. Experimen...

The correlation between transport properties across subnanometric metallic gaps and the optical response of the system is a complex effect that is determined by the fine atomic-scale details of the junction structure. As experimental advances are progressively accessing transport and optical characterization of smaller nanojunctions, a clear connection between the structural, electronic, and optical properties in these nanocavities is needed. Using ab initio calculations, we present here a study of the simultaneous evolution of the structure and the optical response of a plasmonic junction as the particles forming the cavity, two Na380 clusters, approach and retract. Atomic reorganizations are responsible for a large hysteresis of the plasmonic response of the system, which shows a jump-to-contact instability during the approach process and the formation of an atom-sized neck across the junction during retraction. Our calculations demonstrate that, due to the quantization of the conductance in metal nanocontacts, atomic-scale reconfigurations play a crucial role in determining the optical response of the whole system. We observe abrupt changes in the intensities and spectral positions of the dominating plasmon resonances and find a one-to-one correspondence between these jumps and those of the quantized transport as the neck cross-section diminishes. These results reveal an important connection between transport and optics at the atomic scale, which is at the frontier of current optoelectronics and can drive new options in optical engineering of signals driven by the motion and manipulation of single atoms., We acknowledge financial support from Projects FIS2013-41184-P and MAT2013-46593-C6-2-P from MINECO. M.B., P.K., F.M., and D.S.P. also acknowledge support from the ANR-ORGAVOLT project and the Euroregion Aquitaine-Euskadi program. M.B. acknowledges support from the Departamento de Educacion of the Basque Government through a Ph.D. grant. P.K. acknowledges financial support from the Fellows Gipuzkoa program of the Gipuzkoako Foru Aldundia through the FEDER funding scheme of the European Union. J.A. also acknowledges support from Grant 70NANB15H321, “PLASMOQUANTUM”, from the US Department of Commerce (NIST).

et al., A vicinal rutile TiO(110) crystal with a smooth variation of atomic steps parallel to the [1-10] direction was analyzed locally with STM and ARPES. The step edge morphology changes across the samples, from [1-11] zigzag faceting to straight [1-10] steps. A step-bunching phase is attributed to an optimal (110) terrace width, where all bridge-bonded O atom vacancies (O vacs) vanish. The [1-10] steps terminate with a pair of 2-fold coordinated O atoms, which give rise to bright, triangular protrusions (S) in STM. The intensity of the Ti 3d-derived gap state correlates with the sum of O vacs plus S protrusions at steps, suggesting that both O vacs and steps contribute a similar effective charge to sample doping. The binding energy of the gap state shifts when going from the flat (110) surface toward densely stepped planes, pointing to differences in the Ti polaron near steps and at terraces., We acknowledge financial support from the Spanish Ministry of Economy (Grants MAT2013-46593-C6-4-P and MAT2013-46593-C6-2-P) and the Basque Government (Grant IT621-13 and IT756-13). M.S. and U.D. acknowledge support from the ERC Advanced Grant “OxideSurfaces”. D.S.P. and M.M. acknowledge support from the Marie Curie ITN “THINFACE” and financial support by the Deutsche Forschungsgemeinschaft. through SFB 1083 “Structure and Dynamics of Internal Interfaces”.

Controlling the strength of the coupling between organic molecules and single atoms provides a powerful tool for tuning electronic properties of single-molecule devices. Here, using scanning tunneling microscopy and spectroscopy (STM/STS) supported by theoretical modeling, we study the interaction of a planar organic molecule (trinaphthylene) with a hydrogen-passivated Ge(001):H substrate and a single dangling bond quantum dot on that surface. The electronic structure of the molecule adsorbed on the hydrogen-passivated surface is similar to the gas phase structure and the measurements show that HOMO and LUMO states contribute to the STM filled and empty state images, respectively. Furthermore, we show that the electronic properties are not significantly affected when the molecule is attached to the single dangling bond, which is in contrast with the strong interaction of the molecule with a dangling bond dimer. Our results show that the dangling bond quantum dots could stabilize organic molecules on a hydrogenated semiconductor without affecting their originally designed gas phase electronic properties. Together with the ability to laterally manipulate the molecules on the surface, this will be advantageous in the construction of single-molecule devices, where the coupling and positioning of the molecules on the substrate could be tuned by a proper design of the surface quantum dot arrays, comprising both single and dimerized dangling bonds., This work was supported by the Polish Ministry for Science and Higher Education, contract no. 0322/IP3/2013/72. The experiment was carried out using equipment purchased with financial support from the European Regional Development Fund within the framework of the Polish Innovation Economy Operational Program (contract no. POIG.02.01.00-12-023/08). ME, AGL and DSP acknowledge funding by the FP7 FET-ICT “Planar Atomic and Molecular Scale devices” (PAMS) project (funded by the European Commission under contract No. 610446), the Spanish Ministerio de Economia y Competitividad (MINECO) (Grant No. MAT2013-46593-C6-2-P) and the Basque Department of Education and the UPV/EHU (Grant No. IT-756-13). MK acknowledges financial support received from the Foundation for Polish Science (FNP). SG acknowledges the support from the National Science Centre, Poland (2014/15/D/ST3/02975). AME acknowledges the MINECO (Grant No. CTQ2013-42106-P). HK acknowledges the A*STAR Computational Resource Centre (A*CRC) for the computational resources and support. RZ acknowledges support received from KNOW (scholarship KNOW/44/SS/RZ/2015).

Construction of single-molecule electronic devices requires the controlled manipulation of organic molecules and their properties. This could be achieved by tuning the interaction between the molecule and individual atoms by local “on-surface” chemistry, i.e., the controlled formation of chemical bonds between the species. We demonstrate here the reversible attachment of a planar conjugated polyaromatic molecule to a pair of unpassivated dangling bonds on a hydrogenated Ge(001):H surface via a Diels–Alder [4+2] addition using the tip of a scanning tunneling microscope (STM). Due to the small stability difference between the covalently bonded and a nearly undistorted structure attached to the dangling bond dimer by long-range dispersive forces, we show that at cryogenic temperatures the molecule can be switched between both configurations. The reversibility of this covalent bond forming reaction may be applied in the construction of complex circuits containing organic molecules with tunable properties., This work was supported by the National Science Centre, Poland (2014/15/D/ST3/02975). The experiment was carried out using equipment purchased with financial support from the European Regional Development Fund within the framework of the Polish Innovation Economy Operational Program (contract no. POIG.02.01.00-12-023/08). ME, AGL and DSP acknowledge funding by the FP7 FET-ICT “Planar Atomic and Molecular Scale devices” (PAMS) project (funded by the European Commission under contract no. 610446), the Spanish Ministerio de Economia y Competitividad (MINECO) (Grant No. MAT2013-46593-C6-2-P) and the Basque Department of Education and the UPV/EHU (Grant No. IT-756-13). MK acknowledges financial support received from the Foundation for Polish Science (FNP). SG acknowledges the support from the Polish Ministry for Science and Higher Education, contract no. 0322/IP3/2013/72. AME acknowledges the MINECO (Grant No. CTQ2013-42106-P). HK acknowledges the A*STAR Computational Resource Centre (A*CRC) for the computational resources and support. CJ acknowledges the MANA NEXT financial support during this work. RZ acknowledges support received from KNOW (scholarship KNOW/44/SS/RZ/2015).

The theoretical modeling of metal-organic interfaces represents a formidable challenge, especially considering the delicate balance of various interaction mechanisms and the large size of the involved molecular species. In the present study, the energies of interface states, which are known to display a high sensitivity to the adsorption geometry and electronic structure of the deposited molecular species, have been used to test the suitability and reliability of current theoretical approaches. Two well-ordered overlayer structures (relaxed and compressed monolayers) of 1,4,5,8-naphthalene-tetracarboxylic acid dianhydride (NTCDA) on Ag(111) have been investigated using two-photon photoemission to derive precise interface-state energies for these closely related systems. The experimental values are reproduced by our density-functional theory (DFT) calculations with two approaches to treat dispersion interactions (semi-empirical correction DFT-D3 and parametrized functional optB88) and basis set approaches (localized numerical atomic orbitals, plane waves) with remarkable accuracy. Our results underline the trustworthiness and some of the limitations of current DFT-based methods regarding the description of geometric and electronic properties of metal-organic interfaces., This work is a project of the SFB 1083 “Structure and Dynamics of Internal Interfaces” funded by the Deutsche Forschungsgemeinschaft DFG (Germany). D.S.-P. acknowledges support from the Spanish MINECO (Spain), MAT2013-46593-C6-2-P.

arXiv:1609.03842v1, We have theoretically investigated the electronic properties of neutral and n-doped dangling bond (DB) quasi-one-dimensional structures (lines) in the Si(001):H and Ge(001):H substrates with the aim of identifying atomic-scale interconnects exhibiting metallic conduction for use in on-surface circuitry. Whether neutral or doped, DB lines are prone to suffer geometrical distortions or have magnetic ground states that render them semiconducting. However, from our study we have identified one exception—a dimer row fully stripped of hydrogen passivation. Such a DB-dimer line shows an electronic band structure which is remarkably insensitive to the doping level, and thus, it is possible to manipulate the position of the Fermi level, moving it away from the gap. Transport calculations demonstrate that the metallic conduction in the DB-dimer line can survive thermally induced disorder but is more sensitive to imperfect patterning. In conclusion, the DB-dimer line shows remarkable stability to doping and could serve as a one-dimensional metallic conductor on n-doped samples., This work is funded by the FP7 FET-ICT “Planar Atomic and Molecular Scale devices” (PAMS) project (funded by the European Commission under contract No. 610446). ME, PB, TF, AGL, and DSP also acknowledge support from the Spanish Ministerio de Economía y Competitividad (MINECO) (Grant No. MAT2013-46593-C6-2-P) and the Basque Dep. de Educación and the UPV/EHU (Grant No. IT-756-13).

In a recent study [M. Feng, et al., ACS Nano, 2011, 5, 8877], it was shown that CO molecules adsorbed on the quasi-one-dimensional O(2 × 1)/Cu(110) surface reconstruction tend to form highly-ordered single-molecule-wide rows along the direction perpendicular to the Cu–O chains. This stems from the peculiar tilted adsorption configuration of CO on this substrate, which gives rise to short-range attractive dipole–dipole interactions. Motivated by this observation, here we study the adsorption of nitric oxide (NO) on O(2 × 1)/Cu(110) and Cu(110) using density functional theory, with the aim of elucidating whether a similar behaviour can be expected for this molecule. We first study NO adsorption on a clean Cu(110) surface, where the role of short-range attractions between molecules has already been pointed out by the observation of the formation of NO dimers by scanning tunnelling microscopy [A. Shiotari, et al., Phys. Rev. Lett., 2011, 106, 156104]. On the clean Cu(110), the formation of dimers along the [1[1 with combining macron]0] direction is favourable, in agreement with published experimental results. However, the formation of extended NO rows is found to be unstable. Regarding the O(2 × 1)/Cu(110) substrate, we observe that NO molecules adsorb in between the Cu–O chains, causing a substantial disruption of the surface structure. Although individual molecules can be tilted with negligible energetic cost along the direction of the Cu–O chains, the interaction among neighbouring molecules was found to be repulsive along all directions and, consequently, the formation of dimers unfavourable., The authors acknowledge support from the Spanish Ministerio de Economa y Competitividad (MINECO) (Grant No. MAT2013-46593-C6-2-P), the Basque Departamento de Educación and the UPV/EHU (Grant No. IT-756-13), and the Deutsche Forschungsgemeinschaft through the Sonderforschungsbereich 1083. AXBR acknowledges support from the Basque Departamento de Educación and the UPV/EHU through a Zabalduz grant.

We have recently developed an ab initio scheme for the calculation of the electronic structure of surfaces. The method is based on the combination of density functional calculations using finite slabs and the use of recursive methods to obtain the Green’s function of the surface. The slab calculations are performed using a linear combination of atomic orbitals as a basis set. From such calculation we directly obtain the surface Hamiltonian in a tight-binding form. Combining this information with that from a bulk calculation of the substrate, we gather all the pieces to construct the Hamiltonian of the semi-infinite system. The surface Green’s function is then computed using the transfer-matrix method and projected onto a wavepacket localized in the surface region. The width and energy of the surface electronic features are obtained from the analysis of such projection. With this approach we get rid of the finite size effects associated with the slab calculations. We have applied this method to the calculation of resonant charge transfer times from adsorbates to metallic substrates. We have focused in the case of core-excited Ar and S on Ru(0 0 0 1) to compare with core-hole clock spectroscopy experiments. We have also used our method to reveal the role of the elastic width in the scanning tunneling spectroscopy measurements of the quasi two-dimensional quantum well state appearing in p(2 × 2) ordered overlayers of Na and Cs on Cu(1 1 1). Here we present a new application of the method to study a more diluted alkali overlayer, the Cu(1 1 1)–(4 × 4)-Na surface. We present results for the relaxed geometries, binding energies, work function change and the position and width of the 3s Na resonance., This work was supported by the Basque Departamento de Educación, Universidades e Investigación, the Basque Departamento de Industria, Comercio y Turismo and the Diputación Foral de Gipuzkoa through the Etortek programme (Grants NANOMATERIALES and NANOTRON), the University of the Basque Country UPV/EHU (Grant No. 9/UPV 00206.215-13639/2001), the Spanish Ministerio de Educación y Ciencia (Grant No. FIS2004-06490-C03-00), and the EU Network of Excellence NANOQUANTA (Grant No. NMP4-CT-2004-500198).

A combined approach of first-principles density-functional calculations and the systematic cluster-expansion scheme is presented. The dipole, quadrupole, and Coulomb matrix elements obtained from ab initio calculations are used as an input to the microscopic many-body theory of the excitonic optical response. To demonstrate the hybrid approach for a nontrivial semiconductor system, the near-bandgap excitonic optical absorption of rutile TiO2 is computed. Comparison with experiments yields strong evidence that the observed near-bandgap features are due to a dipole-forbidden but quadrupole-allowed 1s-exciton state., 14 pages, 4 figures

arXiv:1512.02104v2, We present a study of the optical response of compact and hollow icosahedral clusters containing up to 868 silver atoms by means of time-dependent density functional theory. We have studied the dependence on size and morphology of both the sharp plasmonic resonance at 3–4 eV (originated mainly from sp-electrons), and the less studied broader feature appearing in the 6–7 eV range (interband transitions). An analysis of the effect of structural relaxations, as well as the choice of exchange correlation functional (local density versus generalised gradient approximations) both in the ground state and optical response calculations is also presented. We have further analysed the role of the different atom layers (surface versus inner layers) and the different orbital symmetries on the absorption cross-section for energies up to 8 eV. We have also studied the dependence on the number of atom layers in hollow structures. Shells formed by a single layer of atoms show a pronounced red shift of the main plasmon resonances that, however, rapidly converge to those of the compact structures as the number of layers is increased. The methods used to obtain these results are also carefully discussed. Our methodology is based on the use of localised basis (atomic orbitals, and atom-centered and dominant-product functions), which bring several computational advantages related to their relatively small size and the sparsity of the resulting matrices. Furthermore, the use of basis sets of atomic orbitals also allows the possibility of extending some of the standard population analysis tools (e.g. Mulliken population analysis) to the realm of optical excitations. Some examples of these analyses are described in the present work., This work is supported, in part, by the ORGAVOLT (ORGAnic solar cell VOLTage by numerical computation) Grant ANR-12-MONU-0014-02 of the French Agence Nationale de la Recherche (ANR) 2012 Programme Modèles Numériques. F Marchesin, P Koval and D Sánchez-Portal acknowledge support from the Deutsche Forschungsgemeinschaft (DFG) through the sfb1083 project, the Spanish mineco MAT2013-46593-C6-2-P project, the Euroregion Aquitaine-Euskadi program and from the Basque Departamento de Educación, upv/ehu (Grant No. IT-756-13). Peter Koval acknowledges financial support from the Fellows Gipuzkoa program of the Gipuzkoako Foru Aldundia through the FEDER funding scheme of the European Union.

This work is licensed under a Creative Commons Attribution 4.0 International License.-- et al., Surface chemistry and catalysis studies could significantly gain from the systematic variation of surface active sites, tested under the very same conditions. Curved crystals are excellent platforms to perform such systematics, which may in turn allow to better resolve fundamental properties and reveal new phenomena. This is demonstrated here for the carbon monoxide/platinum system. We curve a platinum crystal around the high-symmetry (111) direction and carry out photoemission scans on top. This renders the spatial core-level imaging of carbon monoxide adsorbed on a 'tunable' vicinal surface, allowing a straightforward visualization of the rich chemisorption phenomenology at steps and terraces. Through such photoemission images we probe a characteristic elastic strain variation at stepped surfaces, and unveil subtle stress-release effects on clean and covered vicinal surfaces. These results offer the prospect of applying the curved surface approach to rationally investigate the chemical activity of surfaces under real pressure conditions., We acknowledge financial support from the Spanish Ministry of Economy (Grants MAT2013-46593-C6-4-P and MAT2013-46593-C6-2-P ), Basque Government (Grants IT621-13 and IT756-13). A.L.W. acknowledges support from the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-SC0012704. AXBR acknowledges support from the Basque Departamento de Educación and the UPV/EHU through the Zabalduz program. AXBR, PCS and DSP acknowledge the Deutsche Forschungsgemeinschaft through the Sonderforschungsbereich 1083.

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY)., The direction and impact parameter dependence of electronic stopping power, along with its velocity threshold behavior, is investigated in a prototypical small-band-gap semiconductor. We calculate the electronic stopping power of H in Ge, a semiconductor with relatively low packing density, using time-evolving time-dependent density-functional theory. The calculations are carried out in channeling conditions with different impact parameters and in different crystal directions for projectile velocities ranging from 0.05 to 0.6 atomic units. The satisfactory comparison with available experiments supports the results and conclusions beyond experimental reach. The calculated electronic stopping power is found to differ in different crystal directions; however, strong impact parameter dependence is observed only in one of these directions. The distinct velocity threshold observed in experiments is well reproduced, and its nontrivial relation with the band gap follows a perturbation theory argument surprisingly well. This simple model is also successful in explaining why different density functionals give the same threshold even with substantially different band gaps., The financial support from MINECO-Spain through Plan Nacional Grant No. FIS2012-37549-C05-01, FPI Ph.D. Fellowship Grant No. BES-2013-063728, and Grant No. MAT2013-46593-C6-2-P along with the EU Grant “ElectronStopping” in the Marie Curie CIG Program is duly acknowledged. SGIker (UPV/EHU, MICINN, GV/EJ, ERDF and ESF) support is gratefully acknowledged.

At low coverage and temperature the water−surface interaction determines the adsorption geometry of the water molecule on the NaCl(100) surface. However, at room temperature the molecules are also able to move on the surface and form islands where the water molecules are held together by hydrogen bonds. As a step toward the description of such complex phenomenology, in this work we have used density functional theory calculations to study the most favorable adsorption geometry of an isolated water molecule and the energy barriers associated with different hopping mechanisms between equivalent adsorption configurations on this surface. We propose different hopping processes that can be classified as translations, if the molecule moves from one adsorption site to the adjacent one, or reorientations, if the molecule only changes its orientation on the surface and remains in the same adsorption site. The straightforward parallel translation of the water molecule along the surface exhibits the highest barrier. All other processes, either translations or reorientations, involve the rotation of the water molecule around certain axes and present much smaller barriers (at least 50% smaller). To obtain a net movement of the molecule along the surface it is always necessary to combine one of these translational and reorientational processes. Such combinations provide favorable and plausible pathways for the diffusion of the water molecule on the NaCl(100) substrate., This work has been supported by the Basque Departamento de Educación, the UPV/EHU (Grant No. 9/UPV 00206.215-13639/2001), the Spanish Ministerio de Educación y Ciencia (Grant No. FIS2004-06490-C3-00), the European Network of Excellence FP6-NoE “NANOQUANTA” (Grant No. 500198-2), and the projects “NANOMATERIALES” and “NANOTRON” funded by the Basque Departamento de Industria, Comercio y Turismo within the ETORTEK program and the Departamento para la Innovación y la Sociedad del Conocimiento from the Diputación Foral de Guipúzcoa.

Dynamical processes are commonly investigated using laser pump–probe experiments, with a pump pulse exciting the system of interest and a second probe pulse tracking its temporal evolution as a function of the delay between the pulses1,2,3,4,5,6. Because the time resolution attainable in such experiments depends on the temporal definition of the laser pulses, pulse compression to 200 attoseconds (1 as = 10-18 s) is a promising recent development. These ultrafast pulses have been fully characterized7, and used to directly measure light waves8 and electronic relaxation in free atoms2,3,4. But attosecond pulses can only be realized in the extreme ultraviolet and X-ray regime; in contrast, the optical laser pulses typically used for experiments on complex systems last several femtoseconds (1 fs = 10-15 s)1,5,6. Here we monitor the dynamics of ultrafast electron transfer—a process important in photo- and electrochemistry and used in solid-state solar cells, molecular electronics and single-electron devices—on attosecond timescales using core-hole spectroscopy. We push the method, which uses the lifetime of a core electron hole as an internal reference clock for following dynamic processes9,10,11,12,13,14,15,16,17,18,19, into the attosecond regime by focusing on short-lived holes with initial and final states in the same electronic shell. This allows us to show that electron transfer from an adsorbed sulphur atom to a ruthenium surface proceeds in about 320 as., We acknowledge support by the staff of MAX-lab, Lund, Sweden, in particular J. N. Andersen and the ARI program. This work was supported by the Deutsche Forschungsgemeinschaft under Schwerpunktprogramm 1093 “Dynamik von Elektronentransferprozessen an Grenzflächen”, the Basque Departamento de Educación, the University of the Basque Country, the Spanish MEC, European Network of Excellence NANOQUANTA, and Max-Planck Awards for Scientific Cooperation to P.M.E. and D.M.

Non-linearities in the electronic stopping power of light projectiles in bulk Al and LiF are addressed from first principles using time-evolving time-dependent density functional theory. In the case of Al, the agreement of the calculations with experiments for H and He projectiles is fair, but a recently observed transition for He from one value of the electronic friction coefficient to a higher value at v ∼ 0:3 a.u. is not reproduced by the calculations. For LiF, better accuracy is obtained as compared with previously published simulations, albeit the threshold remains overestimated. © 2013 Elsevier B.V. All rights reserved., D.S.P. acknowledges the Basque Departamento de Educación, UPV/EHU (Grant No. IT-366-07), the Spanish Ministerio de Educación y Ciencia (Grant No. FIS2010-19609-C02-00), and the ETORTEK research program funded by the Basque Departamento de Industria and the Diputación Foral de Gipuzkoa.

We have performed a density functional study of fifteen different structural models of the Si(557)-Au surface reconstruction. Here we present a brief summary of the main structural trends obtained for the more favourable models, focusing afterwards in a detailed description of the atomic structure, electronic properties and, simulated STM images of the most stable model predicted by our calculations. This structure is in very good agreement with that recently proposed from X-ray diffraction measurements by Robinson et al. [Phys. Rev. Lett. 88, (2002) 096194]., Comment: 12 pages, including two figures, in preprint format. Submitted to Surface Science on July 2002 (Proceedings of the ECOSS-21 conference)

In this paper we review some recent results on the electronic structure of III-VI layered semiconductors and its dependence under pressure, stressing the specific features that differentiate their behaviour from that of tetrahedrally coordinated semiconductors. We will focus on several unexpected results that have led to changes in the image that was currently accepted a few years ago. Intralayer bond angles change under pressure and the layer thickness remains virtually constant or increases. As a consequence, models based in intra- and inter-layer deformation potentials fail in explaining the low pressure nonlinearity of the band gap. Numerical-atomic-orbital/density-functional-theory electronic structure calculations allow for an interpretation of the evolution of the absorption edge under pressure. In particular, they show how the structure of the non-degenerated valence band maximum in InSe becomes more complex under pressure leading to a non-conventional direct-to-indirect crossover. The valence band maximum in InSe above 4 GPa exhibits a quite singular feature: a ring-shaped constant energy surface and, consequently, a density of states depending on energy as in 2D electronic systems.

This work is licensed under a Creative Commons Attribution 4.0 International License., We present a combined experimental and theoretical study of the electronic properties of close-spaced dangling-bond (DB) pairs in a hydrogen-passivated Si(001):H p-doped surface. Two types of DB pairs are considered, called >cross> and >line> structures. Our scanning tunneling spectroscopy (STS) data show that, although the spectra taken over different DBs in each pair exhibit a remarkable resemblance, they appear shifted by a constant energy that depends on the DB-pair type. This spontaneous asymmetry persists after repeated STS measurements. By comparison with density functional theory (DFT) calculations, we demonstrate that the magnitude of this shift and the relative position of the STS peaks can be explained by distinct charge states for each DB in the pair. We also explain how the charge state is modified by the presence of the scanning tunneling microscopy (STM) tip and the applied bias. Our results indicate that, using the STM tip, it is possible to control the charge state of individual DBs in complex structures, even if they are in close proximity. This observation might have important consequences for the design of electronic circuits and logic gates based on DBs in passivated silicon surfaces., This work is funded by the FP7 FET-ICT “Planar Atomic and Molecular Scale devices” (PAMS) project (funded by the European Commission under contract No. 610446). ME, TF, AGL and DSP also acknowledge support from the Spanish Ministerio de Economía y Competitividad (MINECO) (Grant No. MAT2013-46593-C6-2-P) and the Basque Dep. de Educación and the UPV/EHU (Grant No. IT-756-13). MK acknowledges financial support received from the Polish National Science Centre for preparation of his PhD dissertation (decision number: DEC-2013/08/T/ST3/00047) and from the Foundation for Polish Science (FNP).

26th International Conference on Atomic Collisions in Solids, A method is presented to compute the dielectric function for extended systems using linear response time-dependent density functional theory. Localized basis functions with finite support are used to expand both eigenstates and response functions. The electron-energy loss function is directly obtained by an iterative Krylov-subspace method. We apply our method to graphene and silicon and compare it to plane-wave based approaches. Finally, we compute electron-energy loss spectrum of C60 crystal to demonstrate the merits of the method for molecular crystals, where it will be most competitive., We acknowledge support from ANR OrgaVolt project. D.S-P. and P.K. acknowledge support from the Basque Departamento de Educación, UPV/EHU (Grant No. IT-366-07), the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-02), the ETORTEK program funded by the Basque Departamento de Industria and the Diputación Foral de Guipuzcoa. D.S-P., P.K. and M.P.L. acknowledge the German DFG through SFB 1083.

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY)., The Bethe-Salpeter equation (BSE) is currently the state of the art in the description of neutral electronic excitations in both solids and large finite systems. It is capable of accurately treating charge-transfer excitations that present difficulties for simpler approaches. We present a local basis set formulation of the BSE for molecules where the optical spectrum is computed with the iterative Haydock recursion scheme, leading to a low computational complexity and memory footprint. Using a variant of the algorithm we can go beyond the Tamm-Dancoff approximation. We rederive the recursion relations for general matrix elements of a resolvent, show how they translate into continued fractions, and study the convergence of the method with the number of recursion coefficients and the role of different terminators. Due to the locality of the basis functions the computational cost of each iteration scales asymptotically as O(N3) with the number of atoms, while the number of iterations typically is much lower than the size of the underlying electron-hole basis. In practice we see that, even for systems with thousands of orbitals, the runtime will be dominated by the O(N2) operation of applying the Coulomb kernel in the atomic orbital representation., We acknowledge support from the Deutsche Forschungsgemeinschaft (DFG) through the SFB 1083 project, the ANR ORGAVOLT project, and the Spanish MINECO MAT2013-46593-C6-2-P project. P.K. acknowledges financial support from the Fellows Gipuzkoa program of the Gipuzkoako Foru Aldundia through the FEDER funding scheme of the European Union, Una manera de hacer Europa. F.F. acknowledges support from the EXTRA programme of the “Universita degli Studi di Milano-Bicocca” and from the Erasmus Placement programme for student mobility.

Electromagnetic field localization in nanoantennas is one of the leitmotivs that drives the development of plasmonics. The near-fields in these plasmonic nanoantennas are commonly addressed theoretically within classical frameworks that neglect atomic-scale features. This approach is often appropriate since the irregularities produced at the atomic scale are typically hidden in far-field optical spectroscopies. However, a variety of physical and chemical processes rely on the fine distribution of the local fields at this ultraconfined scale. We use time-dependent density functional theory and perform atomistic quantum mechanical calculations of the optical response of plasmonic nanoparticles, and their dimers, characterized by the presence of crystallographic planes, facets, vertices, and steps. Using sodium clusters as an example, we show that the atomistic details of the nanoparticles morphologies determine the presence of subnanometric near-field hot spots that are further enhanced by the action of the underlying nanometric plasmonic fields. This situation is analogue to a self-similar nanoantenna cascade effect, scaled down to atomic dimensions, and it provides new insights into the limits of field enhancement and confinement, with important implications in the optical resolution of field-enhanced spectroscopies and microscopies., We acknowledge financial support from projects FIS2013-14481-P and MAT2013-46593-C6-2-P from MINECO. M.B., P.K., F.M., and D.S.P. also acknowledge support from the ANR-ORGAVOLT project and the Euroregion Aquitaine-Euskadi program. M.B. acknowledges support from the Departamento de Educacion of the Basque Government through a PhD grant, as well as from Euskampus and the DIPC at the initial stages of this work. R.E. and P.K. acknowledge financial support from the Fellows Gipuzkoa program of the Gipuzkoako Foru Aldundia through the FEDER funding scheme of the European Union, “Una manera de hacer Europa”.

The controlled assembly of metal nanoparticles into macroscopic materials using DNA oligonucleotides has opened new directions of research in nanoscience and nanotechnology. Here, we describe recent ab initio calculations on structural and electronic properties of the subsystems forming these materials: bare and thiol-passivated gold nanoclusters, gold nanowires and fragments of DNA chains. Our results indicate that gold nanoclusters are distorted dramatically by a passivating methylthiol monolayer, that monatomic gold chains are stable in zigzag geometries and that dry acidic λ-DNA is a good insulator. These results provide useful insights towards the complete understanding, design and proper utilization of hybrid DNA-gold nanostructured materials.

Recent advances in both first principles computational methodologies for complex systems and qualitative understanding of the electronic structure of solids now make a real dialogue between theoreticians and experimentalists possible. We discuss how this situation can lead to a fruitful interplay in inorganic solid state chemistry, considering selected examples, such as the structure of gold nanoclusters and nanowires, the absorption of atoms and molecules and growth of thin films on silicon surfaces, understanding the development of some structural modulations in low-dimensional transition metal oxides and bronzes, and the control of the transport properties of hybrid organic–inorganic charge transfer molecular solids.

Inelastic neutron scattering (INS) and single crystal diffraction measurements of tetramethylbenzene (durene) are reported along with first-principles calculations, based on density functional theory (DFT), of structure and dynamics. Atomic positions obtained from refinement of the neutron scattering data and from three different DFT methodologies are in excellent agreement. Normal modes and INS spectra are calculated within the harmonic approximation using the direct cell finite displacement technique. DFT affords a reliable description of intramolecular and intermolecular interactions with the result that the vibrational spectra are well reproduced by all calculations. The advantage over traditional ab initio, single molecule calculations is the improved description of the low frequency vibrations that are influenced by intermolecular interactions. No refinement of force constants has been undertaken. This structural and vibrational analysis is discussed in the context of optical work in durene host lattices.

We present a theoretical study of the electronic and magnetic properties of iron systems in different environments: pure iron systems @dimer, bcc bulk, ~100! surface, and free-standing iron monolayer#, and lowdimensional iron systems deposited on Ag ~100! surface ~monoatomic linear wires, iron monolayer, planar, and three-dimensional clusters!. Electronic and magnetic properties have been calculated using a recently developed total-energy first-principles method based on density-functional theory with numerical atomic orbitals as a basis set for the description of valence electrons and nonlocal pseudopotentials for the atomic core. The Kohn-Sham equations are solved self-consistently within the generalized gradient approximation for the exchange-correlation potential. Tests on the pseudopotential, the basis set, grid spacing, and k sampling are carefully performed. This technique, which has been proved to be very efficient for large nonmagnetic systems, is applied in this paper to calculate electronic and magnetic properties of different iron nanostructures. The results compare well with previous ab initio all-electron calculations and with experimental data. The method predicts the correct trends in the magnetic moments of Fe systems for a great variety of environments and requires a smaller computational effort than other ab initio methods.

Knowledge of the structure of clusters is essential to predict many of their physical and chemical properties. Using a many-body semiempirical Gupta potential (to perform global minimizations), and first-principles density functional calculations (to confirm the energy ordering of the local minima), we have recently found [Phys. Rev. Lett. 81, 1600 (1998)] that there are many intermediate-size disordered gold nanoclusters with energy near or below the lowest-energy ordered structure. This is especially surprising because we studied ''magic'' cluster sizes, for which very compact-ordered structures exist. Here, we show how the analysis of the local stress can be used to understand the physical origin of this amorphization. We find that the compact ordered structures, which are very stable for pair potentials, are destabilized by the tendency of metallic bonds to contract at the surface, because of the decreased coordination. The amorphization is also favored by the relatively low energy associated to bondlength and coordination disorder in metals. Although these are very general properties of metallic bonding, we find that they are especially important in the case of gold, and we predict some general trends in the tendency of metallic clusters towards amorphous structures. (c) 2000 The American Physical Society.

Gold nanoclusters with disordered and ordered structures are obtained as the lowest-energy configurations of the cluster potential energy surface (PES) by unconstrained dynamical and genetic/symbiotic optimization methods using an n-body Gupta potential and first-principle calculations [Phys. Rev. Lett. 81, 1600 (1998)]. In this paper, we report the distribution of lowest-energy minima which characterize the PES of the Au38 cluster, and a comparison of structural and thermal stability properties among several representative isomers is presented. Coexistence among different cluster isomeric structures is observed at temperatures around 250 K. The structure factor calculated from the most stable (lowest-energy) amorphous-like cluster configuration is in better agreement with the X-ray powder-diffraction experimental measurements than those calculated from ordered structures.

We discuss the application of the local-spin-density approximation (LSDA) and provide criteria to gauge the reliability of supercell models of $a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ and tetrahedral amorphous carbon $(ta\ensuremath{-}\mathrm{C}).$ We identify models of $a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ that exhibit a localization on dangling bond consistent with electron-spin-resonance (ESR) experiments and show that a LSDA level description of the electron states is essential to describe these states. We offer an ab initio calculation of a well-isolated floating bond state and show that neither the charge nor spin is well localized. Finally, we suggest the origin of the ESR signal in $ta\ensuremath{-}\mathrm{C}$ is $\ensuremath{\pi}$-bonded pairs at the Fermi level.

Bonding and diffusion of a Ba adatom on a Si(001) surface have been studied using first-principles density-functional calculations. It is found that the favorable bonding site of the adatom is the fourfold site located in the trough between Si dimer rows. The bonding between Ba adatom and the surface is shown to be only slightly ionic in character, with a small charge transfer from Ba to the substrate, and with an important covalent component. The calculated jumping rates show a strongly anisotropic diffusivity of Ba on the surface.

We report ab initio molecular dynamics simulations of ${\mathrm{Ni}}_{2},$ ${\mathrm{Al}}_{2},$ ${\mathrm{Ni}}_{13},$ ${\mathrm{Al}}_{13},$ and ${\mathrm{Ni}}_{12}\mathrm{Al}$ clusters using SIESTA, a fully self-consistent density-functional method that employs linear combinations of atomic orbitals as basis sets, standard norm-conserving pseudopotentials and a generalized-gradient approximation to exchange and correlation. Our results for the pure Ni and Al clusters, which are compared with those obtained by other recent ab initio calculations, are in good agreement with available experimental data. For the binary cluster ${\mathrm{Ni}}_{12}\mathrm{Al}$ our calculations show that a distorted icosahedral configuration with the Al atom at the cluster surface is more stable than that with the Al atom located at the central site, a result that clarifies discrepancies between the results of different semiempirical treatments.

The theoretical scanning-tunneling-spectroscopy image catalog of quantized molecular orbitals of finite armchair carbon nanotubes deposited on a gold (111) surface is presented. Just four different three-dimensional standing-wave (SW) patterns are obtained for electrons close to the Fermi level. The experimental observations of a SW modulation of 0.74 nm and peak pairing in line scans are understood in sight of our results. We show that SW patterns can be explained in terms of the simple H\"uckel model, but the associated energies, relevant to spectroscopic and transport measurements, are very sensitive to different effects beyond that model including the relaxed geometry, the electronic self-consistency in the finite tubes, and the interaction with the substrate.

The lowest energy structures of ${\mathrm{Au}}_{n}$ ( $n\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}38,55,75$) nanoclusters are obtained by unconstrained dynamical and genetic-symbiotic optimization methods, using a Gupta $n$-body potential. A set of amorphous structures, nearly degenerate in energy, are found as the most stable configurations. Some crystalline or quasicrystalline isomers are also minima of the cluster potential energy surface with similar energy. First principles calculations using density functional theory confirm these results and give different electronic properties for the ordered and disordered gold cluster isomers.

We investigate the scattering of surface electrons by the edges of graphene islands grown on Ni(111). By combining local tunneling spectroscopy and ab initio electronic structure calculations we find that the hybridization between graphene and Ni states results in strongly reflecting graphene edges. Quantum interference patterns formed around the islands reveal a spin-dependent scattering of the Shockley bands of Ni, which we attribute to their distinct coupling to bulk states. Moreover, we find a strong dependence of the scattering amplitude on the atomic structure of the edges, depending on the orbital character and energy of the surface states. © 2014 American Physical Society., We acknowledge support from the Basque Departamento de Educación, UPV/EHU (Grants No. IT-366-07 and No. IT-756-13), the Spanish Ministerio de Ciencia e Innovación (Grants No. FIS2010-19609-C02-00, and No. MAT2010-15659), the ETORTEK program funded by the Basque Departamento de Industria, the European Research Council (StG 203239 NOMAD), and Agència de Gestió d’Ajuts Universitaris i de Recerca (2009 SGR 695). A. M. acknowledges funding from the Ramón y Cajal Fellowship program.

We use inelastic electron tunneling spectroscopy first-principles simulations to identify the different chemical bonds present at metal-molecule junctions. We unambiguously identify the nature of these bonds from two distinctive features in the calculated spectra: (i) the presence (or absence) of active vibrational modes and (ii) the dependence of vibrational frequencies on electrode separation. We use this method to present a study of the vibrational properties of alkanes bound to the electrodes via highly conducting Au-C links. In the experiment, these links were formed from molecules synthesized with trimethyl-tin (SnMe3) terminations, where the SnMe3 groups were removed in situ at the junction, in a process involving both breaking and formation of bonds [Cheng, Z.-L.; Skouta, R.; Vázquez, H.; Widawsky, J. R.; Schneebeli, S.; Chen, W.; Hybertsen, M. S.; Breslow, R.; Venkataraman, L. Nat. Nanotechnol. 2011, 6, 353-357]. We obtain the vibrational fingerprint of these direct Au-alkane 0links and extend this study to the other scenario considered in that paper (bonding via SnMe2 groups), which may be relevant under other experimental conditions. We also explore the effect of deuteration on inelastic electron tunneling spectroscopy (IETS). Complete deuteration of the molecules diminishes the differences of the spectra corresponding to the two bonding geometries, making identification more difficult. IETS of an isolated SnMe3 fragment provides an additional basis for comparison in the characterization of the molecular junction., H.V. acknowledges financial support from the Academy of Sciences of the Czech Republic through the J.E. Purkyně fellowship. G.F., D.S.-P., A.A., and T.F. acknowledge the support of the Basque Departamento de Educacion and the UPV/EHU (Grant No. IT-756-13) and the Spanish Ministerio de Economia y Competitividad (Grant No. FIS2013-48286-C2-2-P and Grant No. MAT2013-46593-C6-2-P). D.S.-P. and T.F. acknowledge the European Union FP7-ICT project PAMS (Contract No. 610446).

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence., Quantum well states of Ag films grown on stepped Au(111) surfaces are shown to undergo lateral scattering, in analogy with surface states of vicinal Ag(111). Applying angle resolved photoemission spectroscopy we observe quantum well bands with zone-folding and gap openings driven by surface/interface step lattice scattering. Experiments performed on a curved Au(111) substrate allow us to determine a subtle terrace-size effect, i.e., a fine step-density-dependent upward shift of quantum well bands. This energy shift is explained as mainly due to the periodically stepped crystal potential offset at the interface side of the film. Finally, the surface state of the stepped Ag film is analyzed with both photoemission and scanning tunneling microscopy. We observe that the stepped film interface also affects the surface state energy, which exhibits a larger terrace-size effect compared to surface states of bulk vicinal Ag(111)crystals., This work was supported in part by the Spanish Ministry of Economy (MINECO) through grants MAT2013–46593-C6–2-P, MAT2013–46593-C6–4-P, MAT2013–46593-C6–5-P, and FIS2010–19609-C02–02, by the German Sonderforschungsbereich SFB 1083, and by the Basque Government through Projects IT-621–13 and IT-756–13. ICN2 acknowledges support from the Severo Orchoa Program (MINECO, Grant SEV-2013-0295).

arXiv:1404.5595v1, We investigate by first-principles simulations the resonant electron-transfer lifetime from the excited state of an organic adsorbate to a semiconductor surface, namely, isonicotinic acid on rutile TiO2(110). The molecule-substrate interaction is described using density functional theory, while the effect of a truly semi-infinite substrate is taken into account by Green's function techniques. Excitonic effects due to the presence of core-excited atoms in the molecule are shown to be instrumental to understand the electron-transfer times measured using the so-called core-hole-clock technique. In particular, for the isonicotinic acid on TiO2(110), we find that the charge injection from the LUMO is quenched, since this state lies within the substrate band gap. We compute the resonant charge-transfer times from LUMO+1 and LUMO+2, and systematically investigate the dependence of the elastic lifetimes of these states on the alignment among adsorbate and substrate states. © 2014 American Chemical Society., We acknowledge support from the MIUR of Italy through PRIN project DSSCX (no. 20104XET32). C.M. thanks CARIPLO Foundation for its support within the PCAM European Doctoral Programme and Pirelli Corimav for his Ph.D. scholarship. D.S.-P. acknowledges support from the Basque Departamento de Educación, UPV/EHU (Grant No. IT-366-07), the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010- 19609-C02-02), the ETORTEK program funded by the Basque Departamento de Industria and the Diputación Foral de Guipuzcoa, the EU through the FP7 PAMS project, and the German DFG through SFB 1083.

We have implemented a linear scaling, fully self-consistent density-functional method for performing first-principles calculations on systems with a large number of atoms, using standard norm-conserving pseudopotentials and flexible linear combinations of atomic orbitals (LCAO) basis sets. Exchange and correlation are treated within the local-spin-density or gradient-corrected approximations. The basis functions and the electron density are projected on a real-space grid in order to calculate the Hartree and exchange–correlation potentials and matrix elements. We substitute the customary diagonalization procedure by the minimization of a modified energy functional, which gives orthogonal wave functions and the same energy and density as the Kohn–Sham energy functional, without the need of an explicit orthogonalization. The additional restriction to a finite range for the electron wave functions allows the computational effort (time and memory) to increase only linearly with the size of the system. Forces and stresses are also calculated efficiently and accurately, allowing structural relaxation and molecular dynamics simulations. We present test calculations beginning with small molecules and ending with a piece of DNA. Using double-z, polarized bases, geometries within 1% of experiments are obtained. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 453–461, 1997

Field emission resonances (FERs) on Cu(100) surface are investigated by means of tunneling regime simulations performed with a plane-wave based transport calculation method. FERs are located near the surface and decay into the vacuum, and their accurate simulation requires a faithful description of vacuum states. This type of simulations is thus not possible using the popular transport methods based on atom-centered localized basis sets and the use of plane waves becomes important. We introduce a procedure to treat self-consistently (SC) the finite bias nonequilibrium problem in tunneling regime. Image potential effects are included in a semiempirical way within the SC calculation. Tunneling through FERs is studied following a practical strategy to approximate the inelastic transmission for states lying in the band gap of the surface. As our approach permits the use of any tip geometry, tip effects on the energy and wave functions of FERs are explored. The method reported here provides an ideal tool for the simulation of FERs aimed at the understanding of experimental STS (scanning tunneling spectroscopy) observations. © 2013 American Physical Society., We acknowledge support from the Basque Departamento de Educación and the UPV/EHU (Grant No. IT-756-13), the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-00), and the ETORTEK program funded by the Basque Departamento de Industria and the Diputación Foral de Gipuzkoa. L.W. Wang is supported by the US DOE/SC/BES under contract No. DE-AC02-05CH11231.

We report on the theoretical study of laser-assisted attosecond photoemission from metals. The full time-dependent quantum approach reveals the role of the resonant interband and nonresonant surface emission processes in formation of final atto-streaking spectra. The present results explain recent experimental data on magnesium and show that the valence band streaking essentially reflects the respective weight of surface and resonant bulk electron ejection. © 2013 American Physical Society., P.M.E. acknowledges partial support from Basque Departamento de Education, Universidades, e Investigation (Grant No. IT-366-07), CONSOLIDER, and the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-00).

We show that chemically synthesized polycyclic aromatic hydrocarbons (PAHs) exhibit molecular plasmon resonances that are remarkably sensitive to the net charge state of the molecule and the atomic structure of the edges. These molecules can be regarded as nanometer-sized forms of graphene, from which they inherit their high electrical tunability. Specifically, the addition or removal of a single electron switches on/off these molecular plasmons. Our first-principles time-dependent density-functional theory (TDDFT) calculations are in good agreement with a simpler tight-binding approach that can be easily extended to much larger systems. These fundamental insights enable the development of novel plasmonic devices based upon chemically available molecules, which, unlike colloidal or lithographic nanostructures, are free from structural imperfections. We further show a strong interaction between plasmons in neighboring molecules, quantified in significant energy shifts and field enhancement, and enabling molecular-based plasmonic designs. Our findings suggest new paradigms for electro-optical modulation and switching, single-electron detection, and sensing using individual molecules. © 2013 American Chemical Society., This work has been supported in part by the Spanish MICINN (MAT2010-14885, FIS2010-19609-C02-00, and Consolider NanoLight.es), the European Commission (FP7-ICT-2009-4-248909-LIMA and FP7-ICT-2009-4-248855-N4E), and the Etortek program. A.M. acknowledges financial support through FPU from the Spanish MEC. P.K. aknowledges support from the CSIC JAE-doc program, cofinanced by the European Science Foundation. P.N. acknowledges support from the Robert A. Welch Foundation (C-1222) and the Office of Naval Research (N00014-10-1-0989).

Density functional theory calculations have been used to analyze the electronic and magnetic properties of ultrathin zigzag graphene nanoribbons (ZGNRs) with different edge saturations. We have compared a symmetric hydrogen saturation of both edges with an asymmetric saturation in which one of the edges is saturated with sulphur atoms or thiol groups, while the other one is kept hydrogen saturated. The adsorption of such partially thiolated ZGNRs on Au(111) has also been explored. We have considered vertical and tilted adsorption configurations of the ribbons, reminiscent of those found for thiolated organic molecules in self-assembled monolayers (SAM) on gold substrates. We have found that saturation with sulphur atoms or thiol groups removes the corresponding edge state from the Fermi energy and kills the accompanying spin polarization. However, this effect is so local that the electronic and magnetic properties of the mono-hydrogenated edge (H-edge) remain unaffected. Thus, the system develops a spin moment mainly localized at the H-edge. This property is not modified when the partially thiolated ribbon is attached to the gold substrate, and is quite independent of the width of the ribbon. Therefore, the upright adsorption of partially thiolated ZGNRs can be an effective way to decouple the spin-polarized channel provided by the H-edge from an underlying metal substrate. These observations might open a novel route to build spin-filter devices using ZGNRs on gold substrates. This journal is © 2013 the Owner Societies., We acknowledge support from Basque Departamento de Educación, UPV/EHU (Grant No. IT-366-07), the Spanish Ministerio de Educación y Ciencia (Grant No. FIS2010-19609-C02-00), and the ETORTEK research program funded by the Basque Departamento de Industria and the Diputación Foral de Gipuzkoa. PCS acknowledges support by the Diputación Foral de Gipuzkoa and to IKERBASQUE, Basque Foundation for Science (48011, Bilbao, Spain).

D. Stradi et al., Monolayer graphene grown on Ru(0001) surfaces forms a superstructure with periodic modulations in its geometry and electronic structure. The large dimension and inhomogeneous features of this superstructure make its description and subsequent analysis a challenge for theoretical modeling based on density functional theory. In this work, we compare two different approaches to describe the same physical properties of this surface, focusing on the geometry and the electronic states confined at the surface. In the more complex approach, the actual moiré structure is taken into account by means of large unit cells, whereas in the simplest one, the graphene moiré is completely neglected by representing the system as a stretched graphene layer that adapts pseudomorphically to Ru(0001). As shown in previous work, the more complex model provides an accurate description of the existing experimental observations. More interestingly, we show that the simplified stretched models, which are computationally inexpensive, reproduce qualitatively the main features of the surface electronic structure. They also provide a simple and comprehensive picture of the observed electronic structure, thus making them particularly useful for the analysis of these and maybe other complex interfaces. © 2013 American Physical Society., Work supported by the MICINN Projects No. FIS2010-15127, No. FIS2010-18847, No. CTQ2010-17006, No. FIS-2010-19609-C09-00, No. ACI2008-0777, No. 2010C-07-25200, and No. CSD2007-00010, the CAM program NANOBIOMAGNET S2009/MAT1726 and the Gobierno Vasco-UPV/EHU Project No. IT-366-07. S.B. acknowledges financial support from MEC under FPU Grant No. AP-2007-00157. D.S. acknowledges financial support from the FPI-UAM grant program.

Understanding the magnetic properties of graphenic nanostructures is instrumental in future spintronics applications. These magnetic properties are known to depend crucially on the presence of defects. Here we review our recent theoretical studies using density functional calculations on two types of defects in carbon nanostructures: substitutional doping with transition metals, and sp3-type defects created by covalent functionalization with organic and inorganic molecules. We focus on such defects because they can be used to create and control magnetism in graphene-based materials. Our main results are summarized as follows: 1. Substitutional metal impurities are fully understood using a model based on the hybridization between the d states of the metal atom and the defect levels associated with an unreconstructed D3h carbon vacancy. We identify three different regimes, associated with the occupation of distinct hybridization levels, which determine the magnetic properties obtained with this type of doping. 2. A spin moment of 1.0 μ B is always induced by chemical functionalization when a molecule chemisorbs on a graphene layer via a single C–C (or other weakly polar) covalent bond. The magnetic coupling between adsorbates shows a key dependence on the sublattice adsorption site. This effect is similar to that of H adsorption, however, with universal character. 3. The spin moment of substitutional metal impurities can be controlled using strain. In particular, we show that although Ni substitutionals are nonmagnetic in flat and unstrained graphene, the magnetism of these defects can be activated by applying either uniaxial strain or curvature to the graphene layer.

arXiv:1301.6489, We use time-dependent density functional theory to calculate the energy loss of an antiproton colliding with a small Al cluster previously excited. The velocity of the antiproton is such that non-linear effects in the electronic response of the Al cluster are relevant. We obtain that an antiproton penetrating an excited cluster transfers less energy to the cluster than an antiproton penetrating a ground state cluster. We quantify this difference and analyze it in terms of the cluster excitation spectrum. © 2013 Elsevier Ltd. All rights reserved., NEK acknowledges support from the CSIC JAE-predoc program, co-financed by the European Science Foundation. We also acknowledge the support of the Basque Departamento de Educación and the UPV/EHU (Grant No. IT-366-07), the Spanish Ministerio de Economía y Competitividad (Grant No. FIS2010-19609-CO2-02) and the ETORTEK program funded by the Basque Departamento de Industria and the Diputación Foral de Gipuzkoa.

The O(2×1)/Cu(110) surface reconstruction of the Cu(110) surface is induced by 0.5 ML of oxygen adsorption and is formed by Cu-O chains running along the [001] direction. Here, we show that hybridization between surface states of the Cu(110) substrate and one-dimensional states of the Cu-O chains is crucial in understanding the electronic structure of this surface. Specifically, the interaction between one occupied antibonding band of the Cu-O chain with O(py) character (y-axis taken along the Cu-O chain direction) and the partially occupied surface state at the Y point of the clean Cu(110) surface with Cu(py) character causes major changes in the electronic structure close to the Fermi energy (EF). This surface state decays very slowly into the bulk and a thick slab is needed to properly describe it, which might explain why the importance of this hybridization has not been recognized so far. In our calculations we obtain two hybrid bands: (i) a fully occupied band that strongly hybridizes with the bulk Cu sp states nearby EF, becoming a very broad resonance, thus explaining why it is not observed in photoemission experiments; (ii) an empty band that acquires surface state character, including its dispersion close to the zone boundary at the Y point. This splitting induces a partial population of the py antibonding band that is necessary to reconcile the calculated charge transfer from the Cu(110) substrate to the Cu-O chain (∼0.5 electrons/f.u.) with the apparently fully occupied band structure of the adsorbed Cu-O chain (consistent with 1 electron transferred per formula unit). © 2013 IOP Publishing Ltd., We acknowledge useful discussions withMFeng and H Petek and support from the Basque Departamento de Educación, UPV/EHU (Grant No. IT-366-07), the Spanish Ministerio de Educación y Ciencia (Grant No. FIS2010-19609-C02-00), and the ETORTEK research program funded by the Basque Departamento de Industria and the Diputación Foral de Gipuzkoa. PCS acknowledges support from the Diputación Foral de Gipuzkoa and from IKERBASQUE, Basque Foundation for Science.