A multi-orbital ionic Hamiltonian is presented to analyze the many-body properties of the d-transition metal atoms. This Hamiltonian considers all the atomic states obeying the first Hund's rule and also includes all orbital degeneracy, as well as the interaction of the atom with a metal. We analyze the solution of this ionic Hamiltonian by means of the equation of Motion method up to the fourth order, V4, in the atom-metal interaction. Equations for the appropriate Green-functions for analyzing the chemical and transport properties of the system are given for different atom occupancies. In particular, we introduce a full analysis of the multi-orbital Hamiltonian including atomic configurations with N, N + 1 and N - 1 electrons, and discuss its Kondo properties. The shells d1, d2 and d3 are analyzed in detail and Kondo energies are deduced in all these cases showing good agreement with the conventional known results.

En los últimos años, ha prevalecido una tendencia en el diseño de aerogeneradores de eje horizontal: el aumento de su tamaño con el fin de maximizar la energía extraída del recurso eólico. La interacción suelo-estructura afecta significativamente el comportamiento de la estructura durante eventos sísmicos. Ignorar esta interacción puede conducir a estimaciones inexactas del comportamiento estructural y, por lo tanto, comprometer la seguridad y la eficiencia de la estructura. Las torres eólicas generalmente utilizan fundaciones superficiales, las cuales pueden sufrir asientos diferenciales permanentes durante la fase de excitación sísmica debido a la degradación de rigidez del suelo donde se apoyan y a que el sistema de cargas debido a la interacción fluido-estructura tiene una componente de vuelco importante, lo que podría significar un riesgo alto para este tipo de estructuras. El propósito de este trabajo es investigar los posibles asentamientos permanentes en torres eólicas sometidas a sismo con el propósito de evaluar el desempeño de la estructura fundada sobre zapatas superficiales.

We develop a phase-space ab-initio formalism to compute Ballistic Electron Emission Spectroscopy current-voltage I(V)'s in a metal-semiconductor interface. We consider injection of electrons into the conduction band for direct bias ($V>0$) and injection of holes into the valence band or injection of secondary Auger electrons into the conduction band for reverse bias ($V<0$). Here, an ab-initio description of the semiconductor inversion layer (spanning hundreds of Angstroms) is needed. Such formalism is helpful to get parameter-free best-fit values for the Schottky barrier, a key technological characteristic for metal-semiconductor rectifying interfaces. We have applied the theory to characterize the Au/Ge(001) interface; a double barrier is found for electrons injected into the conduction band -- either directly or created by the Auger process -- while only a single barrier has been identified for holes injected into the valence band.

We report an experimental and theoretical study of the electron-phonon coupling for alpha-Sn/Ge(111), a ./ ./ prototypical triangular lattice surface, closely related to Sn/Si(111)-( 3 x 3), where recent experimental evidence has found superconductivity [X. Wu et al., Phys. Rev. Lett. 125, 117001 (2020)]. We concentrate our study on the (3 x 3) phase of alpha-Sn/Ge(111) that appears between 150 and 120 K and has a well-known geometry with a half-filled electronic band around the Fermi energy. We show that this surface presents a giant electron-phonon interaction that can be considered at least partially responsible for the different phases that this system shows at very low temperature. Our theoretical results indicate that indeed the electron-phonon interaction in alpha-Sn/Ge(111)-(3 x 3) is unusually large, since we find that lambda, the electron mass enhancement for the half-filled band, is lambda = 1.3. This result is in good agreement with the experimental value obtained from high-resolution angle-resolved photoemission spectroscopy measurements, which yield lambda = 1.45 +/- 0.1.

Density functional theory (DFT) is usually formulated in terms of the electron density as a function of positionn(r). Here we discuss an alternative formulation of DFT in terms of the orbital occupation numbers {nα} associated with a local-orbital orthonormal basis set {ϕα}. First, we discuss how the building blocks of DFT, namely the Hohenberg-Kohn theorems, the Levy-Lieb approach and the Kohn-Sham method, can be adapted for a description in terms of {nα}. In particular, the total energy is now a function of {nα},E[{nα}], and a Kohn-Sham-like Hamiltonian is derived introducing the effects of the electron-electron interactions via effective potentials,{Vαeff=∂Eee[{nβ}]/∂nα}. In a second step we consider the Hartree and exchange energies and discuss how to describe them, in the spirit of a DFT approach, in terms of the orbital occupation numbers. In this contribution special attention is paid to the description of the (intra-atomic) correlation energy and corresponding correlation potentials {Vcorr,α}. For this purpose, a model system is analyzed in detail, whereby an atomic Hamiltonian interacts with the environment via a simplified model; the use of this model allows us to obtain the correlation energy and potentials (in terms of {nα}) for different cases corresponding to low, intermediate and high electron correlations.

An extended ionic Hamiltonian for d(5)-transition metal atoms, that incorporates both the effect of the first Hund rule and the effect of the orbital degeneracy in the ground state, is presented. We also discuss a Green-function method to analyze that Hamiltonian, solved by means of the Equation of Motion method. Results for different cases in a V-2 and aV(4)-order are given and, in particular, Kondo frequencies are calculated for atoms with an orbital singlet state or with a multi-orbital degeneracy. The effect of the multi-orbital degeneracy is shown to be important.

In the conventional DFT + U approach, the mean field solution of the Hubbard Hamiltonian associated with thedorf(iσ) electrons of a transition metal atom is used to define the DFT + U potential acting on theiσ-electrons. In this work, we go beyond that mean field solution by analyzing the correlation energy and potential for a multi-level atom described by a Kanamori Hamiltonian connected to different channels representing the environment. As a first step, we analyze the many-body solution of our model, using a local-orbital density functional formalism that takes as independent variables the orbital occupancies,niσ, of the atomic orbitals; accordingly, we present the corresponding density functional solution describing the correlation energy and potential as a function ofniσ. Then, we use this analysis to introduce a DFT + U potential extending previous proposals to materials with arbitrarily high correlation. In particular, we find that this potential mainly screens the conventional mean field potential contribution, and also yields new terms associated with the number of atomic electrons. Our results show that the atomic correlation effects enhance the role played by the intra-atomic exchange interaction and favor the formation of magnetic solutions.

Utilizando un elemento finito especialmente formulado sin una teoría de láminas específica, o sea aplicable a cualquier situación de placa/lámina, se realizó el modelado y la aplicación de la correspondiente presión de diseño a una estructura tipo contención nuclear, modelando además todos los tubos correspondientes a las penetraciones, así como la cimentación y la construcción interna. Primero se hicieron modelos simplificados en diferentes situaciones para obtener valores de referencia. Los resultados obtenidos arrojan unos valores de tensión (membrana+flexión+pico) sobre todo el conjunto, sin necesidad de efectuar submodelos, en un tiempo de cálculo de aprox. 3200 segundos/2 Cores para una malla de aprox. 180 mil nodos.

Macroscopic current-voltage measurements and nanoscopic ballistic electron emission spectroscopy (BEES) have been used to probe the Schottky barrier height (SBH) at metal/Ge(100) junctions for two metal electrodes (Au and Pt) and different metallization methods, specifically, thermal-vapor and laser-vapor deposition. Analysis of macroscopic current-voltage characteristics indicates that a SBH of 0.61-0.63 eV controls rectification at room temperature. On the other hand, BEES measured at 80 K reveals the coexistence of two distinct barriers at the nanoscale, taking values in the ranges 0.61-0.64 and 0.70-0.74 eV for the cases studied. For each metal-semiconductor junction, the macroscopic measurement agrees well with the lower barrier found with BEES. Ab initio modeling of BEES spectra ascribes the two barriers to two different atomic registries between the metals and the Ge(100) surface, a significant relevant insight for next-generation highly miniaturized Ge-based devices.

Two-dimensional melting is one of the most fascinating and poorly understood phase transitions in nature. Theoretical investigations often point to a two-step melting scenario involving unbinding of topological defects at two distinct temperatures. Here, we report on a novel melting transition of a charge-ordered K-Sn alloy monolayer on a silicon substrate. Melting starts with short-range positional fluctuations in the K sublattice while maintaining long-range order, followed by longer-range K diffusion over small domains, and ultimately resulting in a molten sublattice. Concomitantly, the charge order of the Sn host lattice collapses in a multistep process with both displacive and order-disorder transition characteristics. Our combined experimental and theoretical analysis provides a rare insight into the atomistic processes of a multistep melting transition of a two-dimensional materials system.

The K/Si(111):B root 3 x root 3 surface, with one K atom per root 3 x root 3 unit cell, is considered a prototypical case of a surface Mott phase at room temperature. Our Density Functional Theory (DFT) Molecular Dynamics (MD) and free energy calculations show, however, a 2 root 3 x root 3 Charge Density Wave (CDW) ground state. Our analysis shows that at room temperature the K atoms easily diffuse along the lines of a honeycomb network on the surface and that the root 3 x root 3 phase appears as the result of the dynamical fluctuations between degenerate CDW states. DFT-MD free energy calculations also show a 2 root 3 x root 3 <--> root 3 x root 3 transition temperature below 90 K. The competing electron-electron and electron-phonon interactions at low temperature are also analyzed; using DFT calculations, we find that the electron-phonon negative-U * is larger than the electron-electron Hubbard U, indicating that the CDW survives at very low temperature.

An ionic Hamiltonian based on the first Hund rule applied to transition metal atoms is reviewed and discussed in detail. The tunneling current between a STM-tip and a transition metal atom is analyzed by means of that Hamiltonian combined with an effective crystal-field effect. We use an equation of motion (EOM) method to calculate that inelastic tunneling current, as well as the Kondo resonance appearing at the Fermi level.We show how an accurate description of its Kondo resonance for the Co/Cu2N(100) system can be achieved by extending the EOM-calculation up to fourth-order in the atom/metal interaction that defines the parameter of expansion in the EOM-equations. These results allow us to calculate also the inelastic tunneling excitation of the atom and the dynamical fluctuations of the atomic spin from S = 3/2 to S = 1.

Although oat cultivation around the Mediterranean basin is steadily increasing, its yield in these regions lags far behind those of Northern Europe. This results mainly from the poor adaptation of current oat cultivars to Mediterranean environments. Local landraces may act as reservoirs of favorable traits that could contribute to increase oat resilience in this region. To aid selection of suitable agro-climate adapted genotypes we integrated genome-wide association approaches with analysis of field assessed phenotypes of genetic variants and of the weight of associated markers across different environmental variables. Association models accounting for oat population structure were applied on either arithmetic means or best linear unbiased prediction (BLUPs) to ensure robust identification of associations with the agronomic traits evaluated. The meta-analysis of the six joint environments (mega-environment) identified several markers associated with several agronomic traits and crown rust severity. Five of these associated markers were located within expressed genes. These associations were only mildly influenced by climatic variables indicating that these markers are good candidates to improve the genetic potential of oat under Mediterranean conditions. The models also highlighted several marker-trait associations, strongly affected by particular climatic variables including high rain pre- or post-heading dates and high temperatures, revealing strong potential for oat adaptation to specific agro-climatic conditions. These results will contribute to increase oat resilience for particular climatic conditions and facilitate breeding for plant adaptation to a wider range of climatic conditions in the current scenario of climate change.

Ab initio nonequilibrium Keldysh formalism based on an N-order renormalization technique is used to compute I (V) ballistic electron emission microscopy characteristics at the Au/Ge(001) interface. Such a formalism quantitatively reproduces precise experimental measurements under ultrahigh vacuum and low- temperature conditions. At T = 0 K, the ballistic current follows the law (V - V-SB)(2.1), V(SB )being the Schottky barrier. At T > 0 K, temperature effects become significant near the onset and must be taken into account to identify an accurate value for V-SB from a best-fit procedure. We find two values for V-SB, 0.67 and 0.75 eV, which we associate with two different atomic registries at the interface.

Resumen. En este trabajo se presenta un modelo simplificado para analizar el comportamiento bidimensional de una viga plana compuesta, conocida como viga Wagner, formada por elementos de viga y un alma que soporta esfuerzos en su plano. En el marco del método de elementos finitos, se propone utilizar elementos de viga deformables por corte para modelar los rigidizadores y elementos de sólido (2D) para modelar el alma. Se asume que el alma puede actuar en forma limitada en compresión y se analizan estrategias para modelar esta situación. Este tipo de vigas son características en estructuras aeronáuticas y su análisis, en modelos sencillos, se realiza suponiendo que los rigidizadores sólo son efectivos en resistir esfuerzos normales, mientras que el alma sólo es efectiva soportando esfuerzos de corte. Interesa analizar en qué medida los resultados, obtenidos con estas hipótesis simplificadas, se aproximan a la realidad, para lo cual se comparan con resultados obtenidos utilizando herramientas numéricas de mayor fidelidad.

En este trabajo se presenta el analisis de un elemento de lamina delgada utilizando una formulacion de Galerkin Discontinuo (GD). El tratamiento de la primera y segunda forma fundamental se formula a traves de un operador diferencial (derivada GD) expresado en coordenadas convectivas. En contraste con otras formulaciones de GD donde las derivadas se calculan con respecto a un sistema de coordenadas cartesiano, las derivadas GD se formulan a nivel elemental en el espacio parametrico. Asi la formulacion utilizada, tiene la ventaja de calcular y guardar informacion a nivel de los puntos de Gauss facilitando la programacion y el ahorro en tiempo de calculo. Las derivadas GD se aplican al campo de vectores de posicion de la superficie media como al campo de directores normales de la lamina, permitiendo tratar geometrias suaves con cambio de material y mallas arbitrarias. En este trabajo se utilizan elementos cuadrilateros cuadraticos con unicamente grados de libertad traslacionales. Para la parte membranal y flexional se utiliza informacion proveniente del elemento principal y de los elementos vecinos. Las ecuaciones de movimiento se resuelven en forma implicita y explicita. Se muestran algunos ejemplos numericos, donde se analizan velocidades de convergencia para distintas densidades de mallas.

In this perspective we present a comprehensive analysis of the energy level alignment at the interface between an organic monolayer (organic = perylenetetracarboxylic dianhydride, PTCDA, zinc tetraphenylporphyrin, Zn-TPP, and tetracyanoquinodimethane, TCNQ) and a prototypical oxide surface, TiO2(110), looking for universal behaviours. PTCDA shows a physisorbed interaction with TiO2 and a small interface dipole potential with its highest occupied molecular orbital (HOMO) energy level located in the oxide energy gap and the lowest occupied molecular orbital (LUMO) energy level located above the oxide conduction band minimum, EC. We analyse how the interface barrier depends on an external bias potential between the organic layer and the oxide surface, Δ, and find for this interface that the screening parameter S = d|(EC - HOMO)|dΔ is close to 1. In the second case, the Zn-TPP monolayer shows a moderate chemisorbed interaction with some charge transfer from the molecule to the oxide and a significant interface dipole potential, in such a way that S decreases to around 0.8. In the TCNQ/TiO2(110) case, the TCNQ molecules present a strong chemical interaction with the oxide; the LUMO energy level is located in the oxide energy gap in such a way that one electron is transferred from the oxide to the organic molecule; we also find that in this case S ≈ 0.5. All these cases can be integrated within a universal behaviour when (EC - HOMO) is calculated as a function of Δ; that function presents a zig-zag curve with a central part having an S-slope, and two plateaus associated with either the LUMO or the HOMO energy levels crossing the oxide Fermi level. In these plateaus, a Coulomb blockade regime arises and a pace charge layer develops in the oxide surface.