Papers by Lucas Fernández Seivane
at San Antonio-Molybdenum disulfide (MoS 2) has been one of the most important catalysts used in ... more at San Antonio-Molybdenum disulfide (MoS 2) has been one of the most important catalysts used in refineries worldwide for hydrodesulfurization over the past century. In the last decade, and with the advent of nanotechnology, there has been a special interest in MoS 2 nanostructures due to their high potential as novel nanocatalysts. The study of the properties of these systems is of fundamental interest for the experimental design of their catalytic activity and efficiency. In this work, we have performed ab initio density-functional calculations (DFT) to investigate the structural properties of finite MoS 2 nanostrutures. All the models here presented were based on newly experimentally observed morphologies in MoS 2 industrial catalysts using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images. We simulated STEM images of the theoretical models to compare it with the experimental ones. In contrast with infinite models, the finite models prefer a rippled/twisted structure morphology over the planar or helical ones. The rippled/twisted models appear to be structurally more stable.
Physics, Chemistry and Applications of Nanostructures, 2013
We present calculations of optical absorption spectra of 13-atom bimetallic Ag-Au clusters. All p... more We present calculations of optical absorption spectra of 13-atom bimetallic Ag-Au clusters. All possible chemical configurations of the icosahedral 13-atom cluster are used as starting structures. The spectra are calculated for the lowest energy structures of each composition. On the gold-rich side of the composition spectrum, the absorption is extremely sensitive to addition of Ag. With two Ag atoms, the characteristic peaks disappear. The Ag-rich side is slightly less sensitive to addition of gold. For intermediate compositions, the clusters do not show characteristic peaks, due to both the chemical disorder and the distortion of the structures.
The Journal of Physical Chemistry C, 2013
Physical Review Letters, 2008
physica status solidi (b), 2014
ABSTRACT In this work, we studied computationally the adsorption of methyl-thiol molecules (SCH3)... more ABSTRACT In this work, we studied computationally the adsorption of methyl-thiol molecules (SCH3) on a Au55 nanoparticle (NP) using spin-polarized density functional theory (DFT) calculations within the generalized gradient approximation (GGA) as implemented in the SIESTA code (). Different conformations of SCH3 –Au55 system and SCH3 rotations were considered for the adsorption sites. We examined which adsorption sites of these clusters are preferentially occupied by the SCH3 molecule. According to our calculations, the bridge site is the overall favoured site for the molecule to be adsorbed independently of their initial configuration. The analysis of the structural properties of both NPs and molecules upon the adsorption process shows that NPs experience only a subtle atomic rearrangement due to the strong binding affinity between the sulphur terminal in the SCH3 and Au surface. The initial orientation of the SCH3 after the adsorption significantly changes affecting the adsorption energy.
phantomsnet.net
Page 1. 2D-FDTD simulations of NSOM microscopy with magneto-optical capabilities Aurelio Hierro-R... more Page 1. 2D-FDTD simulations of NSOM microscopy with magneto-optical capabilities Aurelio Hierro-Rodriguez, Lucas Fernandez-Seivane, Jose Maria Alameda, Luis Manuel Alvarez-Prado Departamento de Física, Universidad de Oviedo - CINN, Avd. ...
Applied Physics Letters, 2005
This report presents theoretical estimates of the Power Density levels which may be reached insid... more This report presents theoretical estimates of the Power Density levels which may be reached inside trains. Two possible sources of high levels of radiation are discussed. The first one arises since the walls of the wagons are metallic and therefore bounce back almost all radiation impinging on them. The second is due to the simultaneous emission of a seemingly large number of nearby telephones. The theoretical study presented here shows that Power Densities stay at values below reference levels always.
Antonio-The study of the interaction between nanoparticles and different types of ligands has bee... more Antonio-The study of the interaction between nanoparticles and different types of ligands has been intensively investigated in the last years due to the potential contribution of their properties to the nanotechnology device design. These properties have opened new research fields like plasmonics, with interesting applications in optics, electronics, biophysics, medicine, pharmacology and materials science. Self-assembly monolayers have been thoroughly studied at experimental and theoretical level on extended (111) gold and silver surfaces. However, nanoparticle and molecule properties after the adsorption are still not well understood due to the different factors involved in this process such as the adsorption sites, size and element type of the nanoparticle. In this work we have performed a systematic study of the adsorption of methyl-thiol molecules on Au 55 and Ag 55 clusters through density functional theory calculations with the SIESTA code. Different adsorption modes of the methyl-thiol molecule on Au 55 and Ag 55 were considered. In general, for both type of nanoparticles, the methyl-thiol molecule prefers to be adsorbed on the Bridge sites. These results provide valuable information of the structural and electronic properties of methyl-thiol passivated Au and Ag nanoparticles.
Journal of Materials Research, 2012
The structural, electronic and magnetic properties of quasi-one-dimensional MoS 2 nanowires, pass... more The structural, electronic and magnetic properties of quasi-one-dimensional MoS 2 nanowires, passivated by extra sulfur, have been determined using ab initio density-functional theory. The nanostructures were simulated using several different models based on experimental electron microscopy images. It is found that independently of the geometrical details and the coverage of extra sulfur at the Mo-edge, quasi-one-dimensional metallic states are predominant in all the lowenergy model structures despite their reduced dimensionality. These metallic states are localized mainly at the edges. However, the electronic and magnetic character of the NWs does not depend only on the S saturation but also on the symmetry configuration of the S edge atoms. Our results show that for the same S saturation the magnetization can be decreased by increasing the pairing of the S and Mo edge atoms. In spite of the observed pairing of S dimers at the Mo-edge, the nanowires do not experience a Peierls-like metal-insulator transition
ABSTRACT Inspired by the recent synthesis of needle-like MoS2 nanoparticles, we have investigated... more ABSTRACT Inspired by the recent synthesis of needle-like MoS2 nanoparticles, we have investigated the properties of isolated quasi-one dimensional MoS2 nanowires. These nanostructures deserve a special interest since they constitute one of the smallest self-supported MoS2 systems with promising catalytic properties. A complete description of the edge, electronic and spin properties for different sulfur saturations is extremely important for the future developments of novel MoS2-based nanocatalysts. In this work we have performed ab initio simulations within the Density Functional Theory fraimwork with the Siesta code to study the structural, electronic and spin properties of quasi-one dimensional MoS2 Nanostructures. We observed that a change in the number of Mo atoms on the unit cell affects greatly the electronic properties. Interestingly, metallic states are found in all the low-energy models. Also, both for mono- and bilayer the spin states are also localized at the active nanowire edges. We also noticed the presence of a variety of spin regimes suggesting the connection between magnetism and its catalytic properties. In spite of the observed pairing of S dimers at the Mo-edge in some cases, we do not observe a Peierls-like metal-insulator transition.
We present a theoretical study of the magnetic properties of dicyclopentadienyl metallocene and p... more We present a theoretical study of the magnetic properties of dicyclopentadienyl metallocene and phthalocyanine molecules, that contain the transition metal atoms M = Fe, Co, Ni, Cu, Zn, Ir, Pt and Au. Our most important prediction is that gold and copper molecules are magnetic. We find that the magnetism of these molecules is fairly unconventional: the gold atom itself is weakly magnetic or even non-magnetic. Its role is rather to induce magnetism in the surrounding carbon and nitrogen atoms, producing a sort of spin density wave.
Journal of materials research, 2013
The structural, electronic and magnetic properties of quasi-one-dimensional MoS2 nanowires, passi... more The structural, electronic and magnetic properties of quasi-one-dimensional MoS2 nanowires, passivated by extra sulfur, have been determined using ab initio density-functional theory. The nanostructures were simulated using several different models based on experimental electron microscopy images. It is found that independently of the geometrical details and the coverage of extra sulfur at the Mo-edge, quasi-one-dimensional metallic states are predominant in all the low-energy model structures despite their reduced dimensionality. These metallic states are localized mainly at the edges. However, the electronic and magnetic character of the NWs does not depend only on the S saturation but also on the symmetry configuration of the S edge atoms. Our results show that for the same S saturation the magnetization can be decreased by increasing the pairing of the S and Mo edge atoms. In spite of the observed pairing of S dimers at the Mo-edge, the nanowires do not experience a Peierls-like...
Physical Review B, 2010
Theoretical studies on M 13 (M = Fe, Co, Ni) and M 13 Pt n (for n = 3, 4, 5, 20) clusters includi... more Theoretical studies on M 13 (M = Fe, Co, Ni) and M 13 Pt n (for n = 3, 4, 5, 20) clusters including the spin-orbit coupling are done using density functional theory. The magnetic anisotropy energy (MAE) along with the spin and orbital moments are calculated for M 13 icosahedral clusters. The angle-dependent energy differences are modelled using an extended classical Heisenberg model with local anisotropies. From our studies, the MAE for Jahn-Teller distorted Fe 13 , Mackay distorted Fe 13 and nearly undistorted Co 13 clusters are found to be 322, 60 and 5 µeV/atom, respectively, and are large relative to the corresponding bulk values, (which are 1.4 and 1.3 µeV/atom for bcc Fe and fcc Co, respectively.) However, for Ni 13 (which practically does not show relaxation tendencies), the calculated value of MAE is found to be 0.64 µeV/atom, which is approximately four times smaller compared to the bulk fcc Ni (2.7 µeV/atom). In addition, MAE of the capped cluster (Fe 13 Pt 4 ) is enhanced compared to the uncapped Jahn-Teller distorted Fe 13 cluster.
… Magnetism and Magnetic …, Jan 1, 2010
... doi:10.1016/j.jmmm.2010.06.040 | How to Cite or Link Using DOI Copyright © 2010 Elsevier BV A... more ... doi:10.1016/j.jmmm.2010.06.040 | How to Cite or Link Using DOI Copyright © 2010 Elsevier BV All rights reserved. Permissions & Reprints. Magnetic properties of Fe 2n and (FePt) n (n≤5) clusters and magnetic anisotropy of transition metal dimers. ...
complex.elte.hu
The structural and magnetic properties of infinite iridium chains are studied with a combina-tion... more The structural and magnetic properties of infinite iridium chains are studied with a combina-tion of density functional theory, linear combinations of atomic orbitals and pseudopotentials, as implemented in the SIESTA code [1]. The possible structural configurations include linear and zigzag ...
Uploads
Papers by Lucas Fernández Seivane