Optical spectra and exciton radiative lifetimes in bulk transition metal dichalcogenides

The optical response of layered transition metal dichalcogenides (TMDCs) exhibits remarkable excitonic properties which are important from both fundamental and device application viewpoints. One of these phenomena is the observation of intralayer/interlayer excitons. While much effort has been done to characterize excitons in monolayer TMDCs and their heterostructures, a quite limited number of works have addressed the exciton spectra of their bulk counterparts. In this work, we employ ab initio many-body perturbation calculations to investigate the exciton dynamics and spectra of bulk 2H-MX2 (M = Mo, W, and X = S, Se). For molybdenum-based systems, we find the presence of interlayer excitons at energies higher than the first bright exciton (XA), with non-negligible strength intensity. Our results also show that interlayer excitons in tungsten-based systems are almost degenerate in energy with XA and possess very small oscillator strengths when compared with molybdenum-based systems. At room temperature, and considering the thermal exciton fine-structure population for the XA-exciton, we estimate effective radiative lifetimes in the range of ∼4-14 ns. For higher energy excitons we predict longer effective lifetimes of tens of nanoseconds.

Cohort profile: the ESC EURObservational Research Programme Non-ST-segment elevation myocardial infraction (NSTEMI) Registry

AIMS

The European Society of Cardiology (ESC) EURObservational Research Programme (EORP) Non-ST-segment elevation myocardial infarction (NSTEMI) Registry aims to identify international patterns in NSTEMI management in clinical practice and outcomes against the 2015 ESC Guidelines for the management of acute coronary syndromes in patients presenting without ST-segment-elevation.

METHODS AND RESULTS

Consecutively hospitalised adult NSTEMI patients (n = 3620) were enrolled between 11 March 2019 and 6 March 2021, and individual patient data prospectively collected at 287 centres in 59 participating countries during a two-week enrolment period per centre. The registry collected data relating to baseline characteristics, major outcomes (in-hospital death, acute heart failure, cardiogenic shock, bleeding, stroke/transient ischaemic attack, and 30-day mortality) and guideline-recommended NSTEMI care interventions: electrocardiogram pre- or in-hospital, pre-hospitalization receipt of aspirin, echocardiography, coronary angiography, referral to cardiac rehabilitation, smoking cessation advice, dietary advice, and prescription on discharge of aspirin, P2Y12 inhibition, angiotensin converting enzyme inhibitor (ACEi)/angiotensin receptor blocker (ARB), beta-blocker, and statin.

CONCLUSION

The EORP NSTEMI Registry is an international, prospective registry of care and outcomes of patients treated for NSTEMI, which will provide unique insights into the contemporary management of hospitalised NSTEMI patients, compliance with ESC 2015 NSTEMI Guidelines, and identify potential barriers to optimal management of this common clinical presentation associated with significant morbidity and mortality.

In vitro evaluation of the cis-[Ru(phen)2(pPDIp)]2+⁎⁎ complex for antimicrobial photodynamic therapy against Sporothrix brasiliensis and Candida albicans

BACKGROUND

Photodynamic therapy (PDT) activates a photosensitizer by visible light to generate cytotoxic oxygen species that lead to cell death. With proper illumination, PDT is often used in applications on superficial and sub-surface lesions. Sporotrichosis infection occurs by Sporothrix fungi which causes a skin wound, worsened by Candida albicans infections. This study investigated the photosensitizing efficiency of the Ru(phen)₂(pPDIp)(PF₆)₂ complex, RupPDIp, against S. brasiliensis and C. albicans.

MATERIAL AND METHODS

RupPDIp efficiency against these fungi was tested using 450 nm (blue light and 36 J/cm²) and 525 nm (green light, 25.2 J/cm²) at 0.05-20 μM concentrations. To ensure PDT effectiveness, control groups were tested in the absence and in the presence of RupPDIp under light irradiation and in the dark.

RESULTS

RupPDIp eliminated both fungi at ≤5.0 μM. Green light showed the best results, eliminating S. brasiliensis and C. albicans colonies at RupPDIp 0.5 μM and 0.05 μM, respectively.

CONCLUSION

RupPDIp is a promising photosensitizer in aPDT, eliminating 10⁶ CFU/mL of both fungi at 450 nm and 525 nm, with lower light doses and concentrations when treated with the green light compared to the blue light.

Using Neural Network Force Fields to Ascertain the Quality of Ab Initio Simulations of Liquid Water

Accurately simulating the properties of bulk water, despite the apparent simplicity of the molecule, is still a challenge. In order to fully understand and reproduce its complex phase diagram, it is necessary to perform simulations at the ab initio level, including quantum mechanical effects both for electrons and nuclei. This comes at a high computational cost, given that the structural and dynamical properties tend to require long timescales and large simulation cells. In this work, we evaluate the errors that density functional theory (DFT)-based simulations routinely incur into due time- and size-scale limitations. These errors are evaluated using neural-network-trained force fields that are accurate at the level of DFT methods. We compare different exchange and correlation potentials for properties of bulk water that require large timescales. We show that structural properties are less dependent on the system size and that dynamical properties such as the diffusion coefficient have a strong dependence on the simulation size and timescale. Our results facilitate comparisons of DFT-based simulation results with experiments and offer a path to discriminate between model and convergence errors in these simulations.

Nanogap-based all-electronic DNA sequencing devices using MoS2 monolayers

The realization of nanopores in atom-thick materials may pave the way towards electrical detection of single biomolecules in a stable and scalable manner. In this work, we theoretically study the potential of different phases of MoS2 nanogaps to act as all-electronic DNA sequencing devices. We carry out simulations based on density functional theory and the non-equilibrium Green's function formalism to investigate the electronic transport across the device. Our results suggest that the 1T'-MoS2 nanogap structure is energetically more favorable than its 2H counterpart. At zero bias, the changes in the conductance of the 1T'-MoS2 device can be well distinguished, making possible the selectivity of the DNA nucleobases. Although the conductance fluctuates around the resonances, the overall results suggest that it is possible to distinguish the four DNA bases for energies close to the Fermi level.

P260 Left ventricular pseudoaneurysm manifesting as syncope

Introduction

Left ventricular (LV) pseudoaneurysms form when cardiac rupture is contained by adherent pericardium or scar tissue. LV pseudoaneurysm is one of the mechanical complications of myocardial infarctions (MI), particularly inferior wall MI.

Although LV pseudoaneurysms are not common, the diagnosis is difficult and they are prone to rupture. Transthoracic echocardiography is commonly used in clinical practice and is usually sufficient to make the diagnosis of LV pseudoaneurysm. Regardless of treatment, patients with LV pseudoaneurysms had a high mortality rate, especially those who did not undergo surgery.

Description of the clinical case

74 years-old woman, with previous history of hypertension, dyslipidaemia and type 2 diabetes and stable coronary disease. In June 2018 the patient underwent coronary angiography that revealed left main and 3 vessels coronary disease, Cardiac revascularization surgery was proposed that the patient refused. The patient was stable during 6 months. Four days before presenting to emergency department the patient mentioned intermittent pre-cordial pain associated with exertion. At admission day she felt intense pre-cordial pain, accompanied by sudoresis and nausea, relieving with sublingual nitrate. The patient was hemodynamically stable at admission. Electrocardiogram showed sinus rhythm 65 bpm with 2mm ST-elevation of inferior leads. Troponin I was positive 30 ng/dL. Echocardiogram revealed marked hypokinesia of inferior and lateral wall with moderate depression of global systolic function ans presence of slight circumferential pericardial effusion (6mm in diastole on lateral wall)

Emergent coronariography was performed and revealed progression of coronary disease of the right coronary artery with sub-occlusion of the mid segment. Cardiac revascularization surgery was proposed and the patient accepted this time. Echocardiogram was repeated during hospitalization revealed a stable pericardial effusion with reduced dimension comparing to admission. After 3 weeks, while waiting surgery in the ward, the patient was a syncope that resulted in fracture of the distal peroneum. Ecocardiogram was performed and revealed a LV posterior wall pseudoaneurysm through a narrow neck in parasternal long axis view and the presence of large pericardial effusion (Fig 1). The patient was submitted to definitive reparative cardiac surgery with pericardium patch and coronary artery bypass graft from left internal mammary to anterior descending coronary artery. The patient recovered well from the cardiac surgery and at 2 months follow up is alive and without signs of heart failure.

This case illustrates the complexity in the management of patients with LV pseudoaneurysm. These patients require substantial critical care, imaging and surgical expertise.

A high clinical index of suspicion is needed to avoid missing the diagnosis LV pseudoaneurysm and transthoracic echocardiography is essential to establish the diagnosis.

Abstract P260 Figure. Fig 1 - LV pseudoaneurysm

Ab initio modelling of spin relaxation lengths in disordered graphene nanoribbons

The spin-dependent transport properties of armchair graphene nanoribbons in the presence of extrinsic spin-orbit coupling induced by a random distribution of nickel adatoms is studied. By combining a recursive Green's function formalism with density functional theory, we explore the influence of ribbon length and metal adatom concentration on the conductance. At a given length, we observed a significant enhancement of the spin-flip channel around resonances and at energies right above the Fermi level. We also estimate the spin-relaxation length, finding values on the order of tens of micrometers at low Ni adatom concentrations. This study is conducted at singular ribbon lengths entirely from fully ab initio methods, providing indirectly evidence that the Dyakonov-Perel spin relaxation mechanism might be the dominant at low concentrations as well as the observation of oscillations in the spin-polarization.

Phase transition and electronic structure investigation of MoS2-reduced graphene oxide nanocomposite decorated with Au nanoparticles

In this work a simple approach to transform MoS₂ from its metallic (1T' to semiconductor 2H) character via gold nanoparticle surface decoration of a MoS₂ reduced graphene oxide (rGO) nanocomposite is proposed. The possible mechanism to this phase transformation was investigated using different spectroscopy techniques, and supported by density functional theory theoretical calculations. A mixture of the 1T'- and 2H-MoS₂ phases was observed from the Raman and Mo 3d high resolution x-ray photoelectron spectra analysis in the MoS₂-rGO nanocomposite. After surface decoration with gold nanoparticles the concentration of the 1T' phase decreases making evident a phase transformation. According to Raman and valence band spectra analyzes, the Au nanoparticles (NPs) induce a p-type doping in MoS₂-rGO nanocomposite. We proposed as a main mechanism to the MoS₂ phase transformation the electron transfer from Mo 4d _xy,xz,yz in 1T' phase to AuNPs conduction band. At the same time, the unoccupied electronic structure was investigated from S K-edge near edge x-ray absorption fine structure spectroscopy. Finally, the electronic coupling between unoccupied electronic states was investigated by the core hole clock approach using resonant Auger spectroscopy, showing that AuNPs affect mainly the MoS₂ electronic states close to Fermi level.

Structure-Property-Performance Relationship of Ultrathin Pd-Au Alloy Catalyst Layers for Low-Temperature Ethanol Oxidation in Alkaline Media

Pd-containing alloys are promising materials for catalysis. Yet, the relationship of the structure-property performance strongly depends on their chemical composition, which is currently not fully resolved. Herein, we present a physical vapor deposition methodology for developing Pd_xAu_1-x alloys with fine control over the chemical composition. We establish direct correlations between the composition and these materials' structural and electronic properties with its catalytic activity in an ethanol (EtOH) oxidation reaction. By combining X-ray diffraction (XRD) and X-ray photelectron spectroscopy (XPS) measurements, we validate that the Pd content within both bulk and surface compositions can be finely controlled in an ultrathin-film regime. Catalytic oxidation of EtOH on the Pd_xAu_1-x electrodes presents the largest forward-sweeping current density for x = 0.73 at ∼135 mA cm^-2, with the lowest onset potential and largest peak activity of 639 A g_Pd^-1 observed for x = 0.58. Density functional theory (DFT) calculations and XPS measurements demonstrate that the valence band of the alloys is completely dominated by Pd particularly near the Fermi level, regardless of its chemical composition. Moreover, DFT provides key insights into the Pd_xAu_1-x ligand effect, with relevant chemisorption activity descriptors probed for a large number of surface arrangements. These results demonstrate that alloys can outperform pure metals in catalytic processes, with fine control of the chemical composition being a powerful tuning knob for the electronic properties and, therefore, the catalytic activity of ultrathin Pd_xAu_1-x catalysts. Our high-throughput experimental methodology, in connection with DFT calculations, provides a unique foundation for further materials' discovery, including machine-learning predictions for novel alloys, the development of Pd-alloyed membranes for the purification of reformate gases, binder-free ultrathin electrocatalysts for fuel cells, and room temperature lithography-based development of nanostructures for optically driven processes.

Spin-orbit coupling prevents spin channel suppression of transition metal atoms on armchair graphene nanoribbons

We investigate the spin-dependent electronic and transport properties of armchair graphene nanoribbons including spin-orbit coupling due to the presence of nickel and iridium adatoms by using ab initio calculations within the spin-polarized density functional theory and non-equilibrium Green's function formalism. Our results indicate that the intensity of the spin-flip precession is a direct consequence of the relaxed adsorption sites of the adatoms. We point out that d orbitals of Ni and Ir result in strong dependence on the spin-conserved and spin-flip transmission probabilities. In particular, we show that the presence of spin-orbit coupling can lead to an enhancement of the transmission probabilities especially around resonances arising due to weak coupling with specific orbitals.

Finite-size correction scheme for supercell calculations in Dirac-point two-dimensional materials

Modern electronic structure calculations are predominantly implemented within the super cell representation in which unit cells are periodically arranged in space. Even in the case of non-crystalline materials, defect-embedded unit cells are commonly used to describe doped structures. However, this type of computation becomes prohibitively demanding when convergence rates are sufficiently slow and may require calculations with very large unit cells. Here we show that a hitherto unexplored feature displayed by several 2D materials may be used to achieve convergence in formation- and adsorption-energy calculations with relatively small unit-cell sizes. The generality of our method is illustrated with Density Functional Theory calculations for different 2D hosts doped with different impurities, all of which providing accuracy levels that would otherwise require enormously large unit cells. This approach provides an efficient route to calculating the physical properties of 2D systems in general but is particularly suitable for Dirac-point materials doped with impurities that break their sublattice symmetry.

Two-dimensional exciton properties in monolayer semiconducting phosphorus allotropes

Excitons play a key role in technological applications since they have a strong influence on determining the efficiency of photovoltaic devices. Recently, it has been shown that the allotropes of phosphorus possess an optical band gap that can be tuned over a wide range of values including the near-infrared and visible spectra, which would make them promising candidates for optoelectronic applications. In this work we carry out ab initio many-body perturbation theory calculations to study the excitonic effects on the optical properties of two-dimensional phosphorus allotropes: the case of blue and black monolayers. We elucidate the most relevant optical transitions, exciton binding energy spectrum as well as real-space exciton distribution, particularly focusing on the absorption spectrum dependence on the incident light polarization. In addition, based on our results, we use a set of effective hydrogenic models, in which the electron-hole Coulomb interaction is included to estimate exciton binding energies and radii. Our results show an excellent agreement between the many-body methodology and the effective models.

Ultrafast charge transfer dynamics pathways in two-dimensional MoS2–graphene heterostructures: a core-hole clock approach

Ultrafast electron delocalization pathways on the MoS₂/graphene heterostructure were elucidated.

Anomalous Temperature Dependence of the Band Gap in Black Phosphorus

Black phosphorus (BP) has gained renewed attention due to its singular anisotropic electronic and optical properties that might be exploited for a wide range of technological applications. In this respect, the thermal properties are particularly important both to predict its room temperature operation and to determine its thermoelectric potential. From this point of view, one of the most spectacular and poorly understood phenomena is indeed the BP temperature-induced band gap opening; when temperature is increased, the fundamental band gap increases instead of decreases. This anomalous thermal dependence has also been observed recently in its monolayer counterpart. In this work, based on ab initio calculations, we present an explanation for this long known and yet not fully explained effect. We show that it arises from a combination of harmonic and lattice thermal expansion contributions, which are in fact highly interwined. We clearly narrow down the mechanisms that cause this gap opening by identifying the peculiar atomic vibrations that drive the anomaly. The final picture we give explains both the BP anomalous band gap opening and the frequency increase with increasing volume (tension effect).

Edge phonons in black phosphorus

Black phosphorus has recently emerged as a new layered crystal that, due to its peculiar and anisotropic crystalline and electronic band structures, may have important applications in electronics, optoelectronics and photonics. Despite the fact that the edges of layered crystals host a range of singular properties whose characterization and exploitation are of utmost importance for device development, the edges of black phosphorus remain poorly characterized. In this work, the atomic structure and behaviour of phonons near different black phosphorus edges are experimentally and theoretically studied using Raman spectroscopy and density functional theory calculations. Polarized Raman results show the appearance of new modes at the edges of the sample, and their spectra depend on the atomic structure of the edges (zigzag or armchair). Theoretical simulations confirm that the new modes are due to edge phonon states that are forbidden in the bulk, and originated from the lattice termination rearrangements.

Black phosphorus is an allotrope of phosphorous that, like graphite, can be exfoliated to create two-dimensional materials. Here, the authors use Raman spectroscopy and density functional theory calculations to investigate the anomalous behaviour of phonons near different black phosphorus edges.

Quantum interference effects in biphenyl dithiol for gas detection

Biphenyl dithiol (BPDT) was examined for the detection of NO, NO2, NH3 and CO gas molecules using the first-principle methods. The quantum interference effects were observed in the transmission, revealing the application of BPDT as a gas sensor.

Energetic stability, STM fingerprints and electronic transport properties of defects in graphene and silicene

Novel two-dimensional materials such as graphene and silicene have been heralded as possibly revolutionary in future nanoelectronics.

Theoretical assessment of feasibility to sequence DNA through interlayer electronic tunneling transport at aligned nanopores in bilayer graphene

Fast, cost effective, single-shot DNA sequencing could be the prelude of a new era in genetics. As DNA encodes the information for the production of proteins in all known living beings on Earth, determining the nucleobase sequences is the first and necessary step in that direction. Graphene-based nanopore devices hold great promise for next-generation DNA sequencing. In this work, we develop a novel approach for sequencing DNA using bilayer graphene to read the interlayer conductance through the layers in the presence of target nucleobases. Classical molecular dynamics simulations of DNA translocation through the pore were performed to trace the nucleobase trajectories and evaluate the interaction between the nucleobases and the nanopore. This interaction stabilizes the bases in different orientations, resulting in smaller fluctuations of the nucleobases inside the pore. We assessed the performance of a bilayer graphene nanopore setup for the purpose of DNA sequencing by employing density functional theory and non-equilibrium Green’s function method to investigate the interlayer conductance of nucleobases coupling simultaneously to the top and bottom graphene layers. The obtained conductance is significantly affected by the presence of DNA in the bilayer graphene nanopore, allowing us to analyze DNA sequences.

Hybridization effects on the out-of-plane electron tunneling properties of monolayers: is h-BN more conductive than graphene?

Electron transport properties through multilayers of hexagonal boron nitride (h-BN) sandwiched between gold electrodes is investigated by density functional theory together with the non-equilibrium Green's function method. The calculated results find that despite graphene being a gapless semimetal and h-BN two-dimensional layer being an insulator, the transmission function perpendicular to the atomic layer plane in both systems is nearly identical. The out-of-plane tunnel current is found to be strongly dependent on the interaction at the interface of the device. As a consequence, single layer h-BN coupled with atomically flat weakly interacting metals such as gold may not work as a good dielectric material, but the absence of sharp resonances would probably lead to more stable out-of-plane electronic transport properties compared to graphene.

Electronic transport in patterned graphene nanoroads

Graphane, hydrogenated graphene, can be patterned into electronic devices by selectively removing hydrogen atoms. The most simple of such devices is the so-called nanoroad, analogous to the graphene nanoribbon, where confinement-and the opening of a gap-is obtained without the need for breaking the carbon bonds. In this work we address the electronic transport properties of such systems considering different hydrogen impurities within the conduction channel. We show, using a combination of density functional theory and non-equilibrium Green's functions, that hydrogen leads to significant changes in the transport properties and in some cases to current polarization.

Strain- and electric field-induced band gap modulation in nitride nanomembranes

The hexagonal nanomembranes of the group III-nitrides are a subject of interest due to their novel technological applications. In this paper, we investigate the strain- and electric field-induced modulation of their band gaps in the framework of density functional theory. For AlN, the field-dependent modulation of the bandgap is found to be significant whereas the strain-induced semiconductor-metal transition is predicted for GaN. A relatively flat conduction band in AlN and GaN nanomembranes leads to an enhancement of their electronic mobility compared to that of their bulk counterparts.

Confinement effects and why carbon nanotube bundles can work as gas sensors

Carbon nanotubes have been at the forefront of nanotechnology, leading not only to a better understanding of the basic properties of charge transport in one dimensional materials, but also to the perspective of a variety of possible applications, including highly sensitive sensors. Practical issues, however, have led to the use of bundles of nanotubes in devices, instead of isolated single nanotubes. From a theoretical perspective, the understanding of charge transport in such bundles, and how it is affected by the adsorption of molecules, has been very limited, one of the reasons being the sheer size of the calculations. A frequent option has been the extrapolation of knowledge gained from single tubes to the properties of bundles. In the present work we show that such procedure is not correct, and that there are qualitative differences in the effects caused by molecules on the charge transport in bundles versus isolated nanotubes. Using a combination of density functional theory and recursive Green's function techniques we show that the adsorption of molecules randomly distributed onto the walls of carbon nanotube bundles leads to changes in the charge density and consequently to significant alterations in the conductance even in pristine tubes. We show that this effect is driven by confinement which is not present in isolated nanotubes. Furthermore, a low concentration of dopants randomly adsorbed along a two-hundred nm long bundle drives a change in the transport regime; from ballistic to diffusive, which can account for the high sensitivity to different molecules.

Intrinsic stability of the smallest possible silver nanotube

Recently, Lagos et al. [Nature Nanotech. 4, 149 (2009)] reported the discovery of the smallest possible Ag nanotube with a square cross section. Ab initio density functional theory calculations strongly support that the stability of these hollow structures is structurally intrinsic and not the result of contamination by light atoms. We also report the first experimental observation of the theoretically predicted corrugation of the hollow structure. Quantum conductance calculations predict a unique signature of 3.6 G0 for this new family of nanotubes.

Disorder-based graphene spintronics

The use of the spin of the electron as the ultimate logic bit-in what has been dubbed spintronics-can lead to a novel way of thinking about information flow. At the same time single-layer graphene has been the subject of intense research due to its potential application in nanoscale electronics. While defects can significantly alter the electronic properties of nanoscopic systems, the lack of control can lead to seemingly deleterious effects arising from the random arrangement of such impurities. Here we demonstrate, using ab initio density functional theory and non-equilibrium Green's functions calculations, that it is possible to obtain perfect spin selectivity in doped graphene nanoribbons to produce a perfect spin filter. We show that initially unpolarized electrons entering the system give rise to 100% polarization of the current due to random disorder. This effect is explained in terms of different localization lengths for each spin channel which leads to a new mechanism for the spin filtering effect that is disorder-driven.

Electronic transport properties of 1,1'-ferrocene dicarboxylic acid linked to Al(111) electrodes

The electronic transport properties of the 1,1'-ferrocene dicarboxylic acid sandwiched between Al(111) electrodes are studied using first-principles methods. The transmission spectra and the current-voltage characteristics are computed for various two-terminal device models and their relation with the electronic structure of the molecule is thoroughly discussed. The current-voltage characteristics are asymmetric, spin-independent, and vary with the anchoring structure of the molecule to the electrodes. A fine-tuning of the molecular conductance can be easily achieved by applying a gate potential, which is included in our simulations. Interestingly, a spin-polarized current can emerge as a consequence of the gate potential with the relative contribution of the two spin channels varying with the bias.

Designing real nanotube-based gas sensors

Using a combination of density functional theory and recursive Green's functions techniques, we present a full description of a large scale sensor, accounting for disorder and different coverages. Here, we use this method to demonstrate the functionality of nitrogen-rich carbon nanotubes as ammonia sensors as an example. We show how the molecules one wishes to detect bind to the most relevant defects on the nanotube, describe how these interactions lead to changes in the electronic transport properties of each isolated defect, and demonstrate that there are significative resistance changes even in the presence of disorder, elucidating how a realistic nanosensor works.

Modeling the effect of dispersed doping agents in carbon nanotubes

Theoretical studies of how the electronic properties of a nanotube are affected by one isolated doping agent is commonly done by ab-initio electronic structure calculations. Although these calculations are essential to understand how the system responds to doping, they are by no means sufficient, since, in reality, a large disordered array of doping agents must be considered. It is then necessary to combine ab-initio techniques with less-computationally-demanding methods if one wishes to describe the real effect of doping on the electronic properties of nanotubes. Here we propose a method that makes use of ab-initio results for single impurities as an input to generate the parameters of the less-demanding tight-binding technique. The method is based on suitable sum rules for the Green functions of the impurity-free nanotubes and does not rely on any fitting scheme. The resulting parametrization allows us to describe disordered systems without losing the important contributions due to charge transfer and screening. Transport properties are subsequentially investigated.

Effect of the continuity of the π conjugation on the conductance of ruthenium-octene-ruthenium molecular junctions

The conductance of a family of ruthenium-octene-ruthenium molecular junctions with different pi conjugation are investigated using a fully self-consistent ab initio approach which combines the nonequilibrium Green's function formalism with density functional theory. Our calculations demonstrate that the continuity of the pi conjugation in the contact region as well as along the molecular backbone affects the junction conductance significantly, showing the advantage of using the ruthenium-carbon double bond as the linkage of conjugated organic molecules.

Conductance oscillations in zigzag platinum chains

Using first principles simulations we perform a detailed study of the structural, electronic, and transport properties of monatomic platinum chains, sandwiched between platinum electrodes. First, we demonstrate that the most stable atomic configuration corresponds to a zigzag arrangement that gradually straightens as the chains are stretched. Second, we find that the averaged conductance shows slight parity oscillations with the number of atoms in the chain. Additionally, the conductance of chains of fixed oscillates as the end atoms are pulled apart, due to the gradual closing and opening of conductance channels as the chain straightens.

Towards molecular spintronics

The ability to manipulate electron spin in organic molecular materials offers a new and extremely tantalizing route towards spin electronics, both from fundamental and technological points of view. This is mainly due to the unquestionable advantage of weak spin-orbit and hyperfine interactions in organic molecules, which leads to the possibility of preserving spin-coherence over times and distances much longer than in conventional metals or semiconductors. Here we demonstrate theoretically that organic spin valves, obtained by sandwiching an organic molecule between magnetic contacts, can show a large bias-dependent magnetoresistance and that this can be engineered by an appropriate choice of molecules and anchoring groups. Our results, obtained through a combination of state-of-the-art non-equilibrium transport methods and density functional theory, show that although the magnitude of the effect varies with the details of the molecule, large magnetoresistance can be found both in the tunnelling and the metallic limit.

Indication of unusual pentagonal structures in atomic-size Cu nanowires

We present a study of the structural and quantum conductance properties of atomic-size copper nanowires generated by mechanical stretching. The atomistic evolution was derived from time-resolved electron microscopy observations and molecular dynamics simulations. We have analyzed the quantum transport behavior by means of conductance measurements and theoretical calculations. The results suggest the formation of an unusual and highly stable pentagonal Cu nanowire with a diameter of approximately 0.45 nm and approximately 4.5 conductance quanta.

An expert system for diagnosis of acute myocardial infarction with ECG analysis

Coronary heart disease is one of the most prevalent and costly health care problems in the world. The early and accurate diagnosis of coronary heart disease is a major problem in emergency settings. However, many primary and secondary hospitals and primary emergency units lack cardiologists on call which makes the diagnosis difficult. This paper describes an expert system for diagnosis of acute myocardial infarction developed to aid physicians without cardiology specialization. Our main goal was to develop an expert system that assists in the diagnosis and indicates the need of hospitalization in a coronary unit.