Papers by Juan José Palacios
Journal of Chemical Theory and Computation, Dec 8, 2022
In this manuscript we present a theoretical framework and its numerical implementation to simulat... more In this manuscript we present a theoretical framework and its numerical implementation to simulate the out-of-equilibrium electron dynamics induced by the interaction of ultrashort laser pulses in condensed-matter systems. Our approach is based on evolving in real-time the density matrix of the system in reciprocal space. It considers excitonic and non-perturbative light-matter interactions. We show some relevant examples that illustrate the efficiency and flexibility of the approach to describe realistic ultrafast spectroscopy experiments. Our approach is suitable for modeling the promising and emerging ultrafast studies at the attosecond time scale that aim at capturing the electron dynamics and the dynamical electron-electron correlations via X-ray absorption spectroscopy.
Bulletin of the American Physical Society, 2007
An ab initio Green's function study of the electron transport properties of the selected meta... more An ab initio Green's function study of the electron transport properties of the selected metal-porphyrin complexes has been performed. Transmission spectra and current-voltage dependence have been calculated for the porphyrin molecule located between gold electrodes in the presence of interaction with metal atoms, which are most common in biochemistry (Fe(II), Fe(III), Mn(II), and Zn(II)). It was shown that the estimated
SciPost physics core, Jan 20, 2023
Angewandte Chemie, Mar 6, 2023
We report on the chemical design of chiral molecular junctions with stress‐dependent conductance,... more We report on the chemical design of chiral molecular junctions with stress‐dependent conductance, whose helicity is maintained during the stretching of a single molecule junction due to the stapling of both ends of the inner helix. In the reported compounds, different conductive pathways are observed, with clearly different conductance values and plateau‐length distributions, attributed to different conformations of the helical structures. The large chiro‐optical responses and the potential use of these molecules as unimolecular spin filters have been theoretically proved using state‐of‐the‐art Density Functional Theory (DFT) calculations, including a fully ab‐initio estimation of the CISS‐originating spin polarization which is done, for the first time, for a realistic molecular system.
Physical review, Sep 20, 2022
Low-temperature scanning tunneling microscopy is used here to study dynamic bonding of gold atoms... more Low-temperature scanning tunneling microscopy is used here to study dynamic bonding of gold atoms on surfaces under low coordination conditions. In the experiments, using an atomically-sharp gold tip, a gold adatom is deposited onto a gold surface with atomic precision either on the first hollow site near a step edge, or far away from it. Classical molecular dynamics simulations at 4.2 K and density functional theory calculations serve to elucidate the difference in the bonding behavior between these two different placements, while also providing information on the crystalline classification of the STM tips based on their experimental performance.
Nanomaterials
We have explored the use of constrained density functional theory (cDFT) for molecular junctions ... more We have explored the use of constrained density functional theory (cDFT) for molecular junctions based on benzenediamine. By elongating the junction, we observe that the energy gap between the ionization potential and the electronic affinity increases with the stretching distance. This is consistent with the trend expected from the electrostatic screening. A more detailed analysis shows how this influences the charge distribution of both the individual metal layers and the molecular atoms. Overall, our work shows that constrained DFT is a powerful tool for studying screening effects in molecular junctions.
Bulletin of the American Physical Society, 2017
(Spain)-Here we explore whether and how the local moments influence electronic transport properti... more (Spain)-Here we explore whether and how the local moments influence electronic transport properties at the atomic scale on Gd and Eu. Both Eu and Gd are known to have local moments associated with their f-electrons. These coexist with itinerant s and d bands that account for their metallic character. We have studied their conductance when only few atoms form the junction between bulk electrodes made out of the very same material. Thousands of measurements show that both metals have an average lowest conductance, attributed to an atom-size contact, below the quantum of conductance. In the case of Eu, unlike other metals, a strong dependence of the atomic conductance on the macroscopic configuration of the contacts is observed. Our DFT for both metals show f bands fully spin polarized and insulating. sp bands are dominant for transport, where d orbitals seem to have a relevant contribution in some cases. On another hand, the strong variability of the atomic conduction of Eu could be explained as a consequence of magnetic disorder due to the f-character of magnetism in this material.
Bulletin of the American Physical Society, 2014
A remarkable theoretical prediction for graphene is that, in theory, it can be permanently magnet... more A remarkable theoretical prediction for graphene is that, in theory, it can be permanently magnetized by the adsorption of H atoms. Unfortunately, this will only be possible if the adsorption is selectively realized in such a way that all H atoms occupy the same sublattice so that the contributions of the H-induced local magnetic moments add up due to the expected ferromagnetic coupling in this situation. Inspired by recent experiments, I will show that such selectivity can be naturally achieved on the graphite surface. Due to the sublattice broken symmetry on the surface, a spontaneous arrangement of the hydrogen atoms where all end up adsorbed on the same sublattice takes place at room temperature in a reasonable time scale. First-principles calculations combined with kinetic Monte Carlo simulations and model Heisenberg-like Hamiltonians derived from them give a complete account of the emergence of this novel ferromagnetism.
In this system we have studied the dependence of the TMR on the tipsurface distance, the position... more In this system we have studied the dependence of the TMR on the tipsurface distance, the position of the tip, and on the bias voltage. Also we present a comparison between the Landauer formalism and the Tersoff-Hamman approach, usually used in this context. Finally we analyse the interaction between Manganese Phthalocyanine (MnPc) molecules on the manganese surface, focusing on the TMR signature and its dependence on the different adsorption sites. [1] J.J. Palacios et. al. Ab-initio Quantum Transport (ANT). alacant.dfa.ua.es
When a magnetic molecule is deposited on a metallic substrate or attached to metallic contacts it... more When a magnetic molecule is deposited on a metallic substrate or attached to metallic contacts its magnetic moment may actually be screened by the conduction electrons due to the Kondo effect. In view of possible applications of molecular magnets such as nanoscale spintronics and magnetic storage devices, it is important to being able to predict whether the Kondo effect will take place or not in a given system. Also one would like to understand in detail how the Kondo effect emerges in a given situation and how it is controlled by the various parameters such as the molecular conformation and the type of substrate. Using a recently developed ab initio approach for molecular devices [1,2] that explicitly takes into account the strong electronic correlations that give rise to the Kondo effect, we have calculated the electronic structure and transport properties of different magnetic molecules coupled to nanocontacts [3] and surfaces [4]. Our calculations shed light on the complex nature of the Kondo effect in molecular-scale devices. [1] D.
recent years, Kondo−like resonances have been measured by different experimental groups in the 3\... more recent years, Kondo−like resonances have been measured by different experimental groups in the 3\2 high spin Manganese Phthalocyanine (MnPc) on different kinds of surfaces [1,3]. With the aim to understand these resonances we have performed Dynamical Mean Field Theory calculations based on models extracted from Density Functional Theory calculations and Green's function formalism [4,5]. Two types of models are considered: one based on atomic d orbitals and one based on frontier molecular orbitals which contain the spin of the molecule.
There has been a great effort in recent years to understand the emerging Kondolike resonances in ... more There has been a great effort in recent years to understand the emerging Kondolike resonances in different magnetic molecules such as MnPc. Theoretical approaches based on atomic models have proven to be very useful for the study of this phenomenon when the magnetic moment is essentially localized on a magnetic atom [1,2]. Nevertheless the Kondo effect can arise in pure carbon-based systems as has been demonstrated experimentally in fullerenes and carbon nanotubes [3,4]. In this communication we present a multiorbital Anderson model where the orbitals are not atomic but molecular orbitals. This model is fully obtained from Density Functional Theory calculation in combination with Green's functions methodologies [5,6]. Standard impurity solver techniques are used to solve the model which is applied to fullerenes and other nanographene structures [7].
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Papers by Juan José Palacios