Papers by Javier Fdez Sanz
Journal of Materials Research, 2022
The optoelectronic properties of several Ag2S/graphene and FeS2/graphene nanostructures are exami... more The optoelectronic properties of several Ag2S/graphene and FeS2/graphene nanostructures are examined through density functional theory calculations including dispersion forces. First, we analyzed the electronic structure of Ag2S and FeS2 nanocluster models, as prototypes of quantum dots, focusing on the electronic structure and absorption spectra. In the case of FeS2 nanoparticle, both ferro- and antiferromagnetic arrangements were considered. Then, Ag2S and FeS2 nanoclusters were adsorbed on top of both graphite and graphene slab models to study the stability of the systems as well as the effect of the nanocluster–surface interaction in the electronic structure, including an insight into the electron injection mechanisms in these systems. Finally, interface models, consisting of Ag2S or FeS2 thin films adsorbed on a graphene layer, were built and their optoelectronic properties examined. Overall, the results obtained in this work, support the suitability of these systems for their ...
Theoretical Chemistry Accounts, 2018
Quantum dot-sensitized solar cells (QDSSCs) are becoming a viable alternative in the market of th... more Quantum dot-sensitized solar cells (QDSSCs) are becoming a viable alternative in the market of the third-generation solar cells. Replacing conventional TiO 2 or ZnO thin films with anatase TiO 2 nanotubes (NTs) leads to a faster charge separation of the excited electron from the quantum dot (QD) to the anode and, consequently, to higher efficiencies. In addition, the adsorption mode of the QDs to the nanotube plays a significant role in the quest for more efficient QDSSCs. We investigate these effects by means of density functional theory (DFT) and real-time time-dependent DFT. Differently sized QDs [(CdSe) 13 and (CdSe) 34 , bare clusters and saturated with methylamine and p-toluidine] are added to different anatase TiO 2 nanotubes [NT(0,8), NT(0,12), NT(0,16)]. We considered direct adsorption or linkage via mercaptopropionic acid (MPA). First, the nanotube diameter does not affect the electronic absorption spectra. When the QDs are linked with MPA, we find that the absorption spectrum resembles that of the single QD. Also, the size of the QD has a significant impact on the absorption spectrum and it can happen that the conduction band (CB) of an unsaturated QD lies below that of the nanotube. Saturation of the QD's surface pushes the CB up again. Furthermore, aromatic ligands increase the first absorption peak maximum to higher energies. Keywords Titanium oxide nanotubes • Solar cells • Quantum dots • Computational modeling • Real-time time-dependent DFT (RT-TDDFT) Published as part of the special collection of articles "In Memoriam of Claudio Zicovich."
Physical Chemistry Chemical Physics, 2018
Here, a new catalyst, Au/TiO2–Y2O3, is presented as an alternative to the less selective Pt/oxide... more Here, a new catalyst, Au/TiO2–Y2O3, is presented as an alternative to the less selective Pt/oxide systems opening the door to new improvements to reduce the operating temperature and the deactivation of these catalysts.
Theoretical Chemistry Accounts, 2017
Dye-sensitized solar cells (DSSCs) have become in one important and promising technology in the p... more Dye-sensitized solar cells (DSSCs) have become in one important and promising technology in the photovoltaic field. The ability for a sensitizer to harvest light photons and inject the excited electrons into a photoanode, typically a metal oxide, determines the performance and operation range of the solar cell. Metal complexes with 1,3dithiole-2-thione-4,5-dithiolate (dmit) ligands, which are an important class of functional materials, have received extensive attention due to their intriguing chemical and physical properties. The electronic and molecular properties of isolated and adsorbed nickel complexes with dmit ligands have been investigated using first principles calculations based on the density functional theory (DFT). Adsorption energies of metal complexes supported on the anatase TiO 2 (101) surface were calculated for three different configurations, linked by sulphur atom of S thione , S thiole-S thiolate , and planar. The most stable adsorption configurations found in this study are the S thiole-S thiolate and the planar forms for the nickel complex. TD-DFT molecular calculations reveal that the lowest energy transition in ultraviolet visible near-infrared (UV-Vis-NIR) mainly corresponds to the HOMO-LUMO π-π* excitation for the nickel complex. The effect of the TiO 2 (101) surface on the absorption spectra of the nickel complex is practically limited to a red shift of about 0.1-0.3 eV. The analysis of the density of states for the dmit/TiO 2 (101) system shows that the LUMO of the metal complex lies at the edge of the TiO 2 conduction band indicating, therefore, that electron injection from the complex excited state into the semiconductor surface is unlikely.
Journal of Molecular Structure: THEOCHEM, 1997
Ab initio calculations of the electron-transfer matrix element Vob in bimetallic model systems [M... more Ab initio calculations of the electron-transfer matrix element Vob in bimetallic model systems [M-M]+ and [M-L-M]' with M = Be, Zn and L = 0, S,-CHzand-CSZ-, are reported. Electron correlation effects are estimated through a second-order method in which only the differential space contributing to the transfer integral Hob is considered. Vob is found to be noticeably larger for bridged systems, showing that the through bond mechanism is pre-eminent in these systems. In most of the calculations, electron correlation contributions are found to increase Vob, the corrections in some cases being as large as 35%. Analysis of the second-order contributions in these cases shows that intruder states involving ligand or metal ligand excitations strongly mix with the zeroth-order model wave functions.
The journal of physical chemistry. B, Jan 17, 2017
In this work, we explore the interaction between some prototypical asphaltene and porphyrin molec... more In this work, we explore the interaction between some prototypical asphaltene and porphyrin molecules with a fully hydroxylated (0001) surface of α-quartz by means of theoretical calculations based on the density functional theory (DFT) under periodic boundary conditions. The influence of dispersion forces, adsorption geometries, and size of the side chain is analyzed. The inclusion of London dispersion forces is overriding as they increase the interaction by about 1 order of magnitude. All of the considered molecules strongly interact with the hydroxylated surface and prefer to adsorb in a parallel position instead of vertically. It is also found that adsorption energy always increases with larger side chains because dispersion interactions also augment. Interestingly, in the case of porphyrin, the less stable isomer in the gas phase is the preferred one after adsorption, which is substantiated by a differential stabilization induced by the surface. Finally, we present a comparativ...
J Mol Struc Theochem, 2004
Atomistic simulations of the structure of Cu atoms supported on the undefective a-Al 2 O 3 (0001)... more Atomistic simulations of the structure of Cu atoms supported on the undefective a-Al 2 O 3 (0001) surface at the low coverage regime are reported. The alumina surface is represented by a slab obtained by imposing periodic boundary conditions to a 8!8!1 supercell (1920 atoms). Classical molecular dynamics simulations at two different coverage and three temperatures are presented. At 1/3 ML, formation of a Cu monolayer is observed with Cu atoms bound to surface oxygen ions and surrounded by six Cu atoms about 4.5 Å far. For the time of simulations these monolayers show stability in the 300-1000 K temperature range, although when the temperature is raised to 1000 K, the radial distribution functions show peaks corresponding to Cu couples sharing the same cell. At coverage 1/6 ML, formation of 2D regions is observed, while Cu atoms sharing cells are not detected whatever the temperature is. The simulations would support a growth mode involving the formation of a monolayer previous to 3D crystallite growth. Preliminary ab initio MD simulations based on density functional calculations at coverage qZ2/3 ML shows that Cu(I) and Cu(0) atoms are disposed as buckled zigzag chains along the three equivalent directions of the lattice.
ACS Catalysis, 2016
Experimental techniques and state-of-the-art DFT calculations have been combined to study the eff... more Experimental techniques and state-of-the-art DFT calculations have been combined to study the effect of the metalsubstrate interaction in the Cu/CeO x /TiO 2 (110) system for the water-gas shift reaction. Experiments demonstrate that OH groups are easily produce in the CeO x /TiO 2 (110) and the importance of highly dispersed Cu clusters in the performance of the catalyst. The apparent activation energy was also calculated and is in agreement with the higher activity of this system compare to other families of catalysts. DFT calculations indicate that CeO x are the preferential nucleation sites for the Cu nanoparticles, improving the dispersion of the metal phase and making available the reservoir of OH groups dissociated in the CeO x clusters. The minimum energy path for the WGS reaction on the new highly active catalytic system Cu/CeO x /TiO 2 (110) has been predicted by state-of-theart theoretical calculations. Main steps as adsorption-dissociation of water, and *OCOH carboxyl intermediate formationdeprotonation have been characterized. In this very particular system, water dissociation is no longer the rate-limiting step since the energy barrier for this process is only 0.04 eV. One important insight of the present work is to show that easy full-hydration of the ceria particles strongly lowers the reaction barrier for the deprotonation of the *OCOH intermediate and facilitates the evolution of the WGS reaction. For the first time, it has been found a system on which the WGS reaction is able to work with all the involved energy barriers below 0.5 eV. This extraordinary behavior makes the Metal/CeO x /TiO 2 family an outstanding candidate for industrial application as catalysts in the WGS reaction.
The Journal of Physical Chemistry, 1990
Surface Sci, 2005
A comparative study of the interaction between single copper, silver and gold atoms and the regul... more A comparative study of the interaction between single copper, silver and gold atoms and the regular Al-terminated a-Al 2 O 3 (0 0 0 1) surface is reported. The surface was simulated by means of periodic slabs and the calculations were undertaken using the spin-polarized density functional theory within the generalized gradient approach. For metal adsorption, five different sites were considered, two on top of Al and O atoms, and three on hollow positions in which the transition metal binds three surface O atoms. Metal-surface interaction is relatively weak with adsorption energies in the range 0.7-1.1 eV, following the order Cu > Au > Ag. The preferred site for Cu and Ag are the three fold hollow oxygen sites while Au atoms prefer to bind the surface on top of the oxygen atoms. Examination of the electron density plots shows that some charge transfer toward the surface takes place according to the sequence Cu > Ag > Au. An analysis of the bond mechanism based on model cluster calculations indicates that for Cu and Ag the largest contribution to the interaction energy arise from the charge transfer from the adsorbed atom to the surface while in the case of Au, the interaction is dominated by the polarization of the transition metal.
Chem Phys Lett, 1992
Molecular dynamics (MD) studies of T-AI203 using a pairwise additive interaction potential of Pau... more Molecular dynamics (MD) studies of T-AI203 using a pairwise additive interaction potential of Pauling's type are reported. MD simulations on a medium-sized cluster of T-AI203 (AI576Oa64) show a picture of its structure which is in agreement with neutron diffraction results and lead to an interpretation of its main properties. MD simulations at several temperatures and velocity autocorrelation functions are also reported.
Journal of the American Chemical Society, 2010
Proceedings of the National Academy of Sciences of the United States of America, 2009
Surface Science, 2016
Abstract We explore the interaction between acetic acid, some typical α-amino acids (α-AAs), and ... more Abstract We explore the interaction between acetic acid, some typical α-amino acids (α-AAs), and a fully hydroxylated (0001) surface of α-quartz by means of theoretical calculations based on the density functional theory (DFT) under periodic boundary conditions. The influence of microsolvation, represented by a water multilayer, and dispersion forces is analyzed. All the considered molecules strongly adsorb on the hydroxylated surface and prefer to adsorb molecularly. The inclusion of dispersion forces increases the interaction energies by 15–30 kJ/mol, without significant changes in structure and mode of adsorption except for histidine where the interaction is improved through protonation of the α-amine group. When the water multilayer is included a decrease in the surface–adsorbate interaction energies is observed. Also, some α-AAs, glycine and alanine, change their adsorption mode and, now, the more stable structure is the zwitterion. Adsorption as zwitterions is always favored with respect to molecular interaction when dispersion forces are taken into account. Comparing the energies of adsorbed and solvated α-AA zwitterions, it turns out that inclusion of dispersion forces predicts that solvated zwitterions are the lower energy configurations.
The Journal of Physical Chemistry, 1992
A spectroscopic and theoretical study of the electronic structure of Fe(CO)s is reported. The vac... more A spectroscopic and theoretical study of the electronic structure of Fe(CO)s is reported. The vacuum-UV electronic spectrum of Fe(CO)5 was recorded in the gas phase at room temperature in the region 210-1 10 nm. The spectrum is dominated by a strong absorption with a maximum at 194 nm, followed by a series of strong overlapped bands of increasing intensity. Ab initio CASSCF CCI calculations of the lowest ligand field, the two first ionization energies, and the first s, p, and d terms of the two first Rydberg series were undertaken. The excellent agreement found between experiment and theory for the LF transition and IEs shows the quantitative accuracy of these calculations. The first Rydberg series arises from excitation of one 3d, electron toward 4s, 4p, and 4d atomic-like orbitals and ranges from 49600 to 61 800 an-'. The term value calculated for the 3d,-4s excitation (18 800 cm-I) is close to that deduced from the first Rydberg transition of iron. The second Rydberg series corresponds to excitation of the 3d, levels and falls in the region comprised between 64 100 and 71 800 cm-l. been carried out on the CRAY-2 computer of the CCVR (Palaiseau, France) through a grant of computer time from the Conseil Scientifique du Centre de Calcul Vectoriel pour la Recherche. This work was partially supported by the Direction General de Investigacion Cientifica y T h i c a (grant PB86-0140). Registry No. Fe(CO)5, 13463-40-6. (3 1) Only eight Rydberg transitions are reported in Table 11. Our attempts to converge the CASSCF procedure on the Rydberg state corresponding to the 3d-4d,2 excitation were unsuccessful. Namely the presence of the state corresponding to the 3d-3d,2 in the same symmetry causes the higher root to collapse into the lowest one. (32) Moore, C. E. Afomic Energy levels; Nat. Bur. Stand. Circ. No. 467; US GPO: Washington DC, 1949.
Journal of Molecular Structure: THEOCHEM, 1993
An ab initio model potential that can be used to substitute for the whole N2 molecule has been de... more An ab initio model potential that can be used to substitute for the whole N2 molecule has been determined and used in Hartree-Fock SCF-MO molecular calculations of the N2. .. HF complex. The results are compared with those obtained from all-electron calculations and a good dependence of the model potential, both in its radial and angular features, is found.
International Journal of Molecular Sciences, 2001
The structure and local electron properties of Au atoms deposited on the TiN (001) surface has be... more The structure and local electron properties of Au atoms deposited on the TiN (001) surface has been theoretically analyzed using a periodic slab model and density functional based calculations. The surface is described by means of a 2x2 cell five layers thick, on which gold atoms are added. Deposition of single atoms on the surface, (θ = 0.25 ML), shows that the preferred site is on-top of Ti atoms, with a metal-surface distance of 2.49 Å. The computed adsorption energy for this site is-1.92 eV, only slightly lower than that lying between two Ti surface atoms (-1.90 eV). The on-top nitrogen sites are less favorable by about 0.4 eV. The calculations were carried out using the Perdew-Wang 91 exchange correlation functional and ultra soft pseudopotentials, with electronic states represented by a plane-wave expansion.
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Papers by Javier Fdez Sanz