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Jorge M Seminario

Publications and source records attributed to Jorge M Seminario.

17 recordsLinked to original sources
PubMed2006

Molecular electrostatic potential devices on graphite and silicon surfaces.

We demonstrate that molecular gates using molecular electrostatic potentials (MEP) can be used on hydrogen-passivated silicon substrates without any disturbance of their behavior in vacuum; however, the use of graphite as a substrate strongly affects such behavior. As expected, the substrate may become one more design variable. The ability to have several substrate alternatives is very important for the practical implementation of this new scenario based on molecular potentials. In general, the effect of the substrate can be predetermined by calculating the MEP of the surface as this indicates how strongly its intrinsic potential is.

Journal Article↗
PubMed2006

Intensity enhancement of the vibrational spectrum of oxygen when attached to a platinum nanocluster.

Detecting single molecules is a technical and scientific challenge and requires to increase the number of molecules or their cross section to a radiation field in order to have a detectable signal. We demonstrate for a single molecule of oxygen that, by attaching the molecule to a nanocluster, the molecule signature spectrum is transferred to the larger complex (molecule cluster). Therefore, the detection can focus on the complex, which can have a much larger cross section, rather than on the small molecule. This is based on the concept of signature transfer, which can be used to detect in the cluster several other properties of the attached molecule.

Journal Article↗
PubMed2006

Platinum testbeds: interaction with oxygen.

We develop testbeds to study catalytic reactions modeled using the minimum number of platinum atoms needed to have an acceptable description of the chemistry on a realistic platinum surface that may include the contribution from a bulk continuum or may simply represent a local site on a nanocluster. In this particular case, the requirement is that a stable cluster may be connected to a stable bulk with equivalent highest occupied molecular orbital and Fermi level, respectively. We focus our work on the interaction of platinum clusters with molecular oxygen, which yields a complex cluster-molecule with fully delocalized molecular orbitals in the neighborhood of the Fermi energy of platinum, responsible for the interesting catalytic behavior of this material.

Journal Article↗
PubMed2006

Adsorption and dissociation of H2O2 on Pt and Pt-alloy clusters and surfaces.

The adsorption of H(2)O(2) on Pt and Pt-M alloys, where M is Cr, Co, or Ni, is investigated using density functional theory. Binding energies calculated with a hybrid DFT functional (B3PW91) are in the range of -0.71 to -0.88 eV for H(2)O(2) adsorbed with one of the oxygen atoms on top Pt positions of Pt(3), Pt(2)M, and PtM(2), and enhanced values in the range of -0.81 to -1.09 eV are found on top Ni and Co sites of the Pt(2)M clusters. Adsorption on top sites of Pt(10) yields a weaker binding of -0.48 eV, whereas on periodic Pt(111) and Pt(3)Co(111) surfaces, H(2)O(2) generally dissociates into two OH radicals. On the other hand, attempts to attach H(2)O(2) on bridge sites cause spontaneous dissociation of H(2)O(2) into two adsorbed OH radicals, suggesting that stable adsorptions on bridge sites are not possible for any of the clusters or extended surfaces that are being studied. We also found that the water-H(2)O(2) interaction reduces the strength of the adsorption of H(2)O(2) on these clusters and surfaces.

Adsorption↗
PubMed2006

Atomistic nature of transient and steady-state responses.

We find experimentally that a system comprised of nanosized features no longer shows fixed steady characteristics as in solid-state devices, and instead, because of the chemistry of the nanostructure, the thermal motion of the atoms, and the external fields, the nanosized system shows intermittent behavior, that is, transient behavior. This transient response for nanosized systems might misguide conclusions regarding observed negative differential resistance (NDR) which is due to the collective nuclei rearrangements to more stable conformations under the presence of an applied field yielding, in many cases, resonances between conformations that can sustain during the steady-state period. This NDR yields peculiar behavior that needs to be considered to design molecular and nanoelectronic devices. In addition, the commonly sharp contrast between transient and steady responses blurs at the nanoscale. In nanosize systems, the time constants or transient response times depend on the velocity of the rearrangements of the atoms in the system or molecule.

Journal Article↗
PubMed2006

Transient behavior at the nanoscale.

Transient and steady state responses of a system to an input are well-known features of materials and systems in science and engineering. These responses depend on the intrinsic parameters of the system and on the nature of the input. We find that a system comprised of nanosized features no longer shows the typical stationary characteristics as their microscopic or solid-state counterparts. Interestingly, because of the chemistry of the nanostructure, thermal motion of the atoms, and external fields, the nanosized system shows extended electrical transient behavior, compatible with highly nonlinear features such a negative differential resistance and hysteresis.

Journal Article↗
PubMed2006

Perfluorobutane sulfonic acid hydration and interactions with O2 adsorbed on Pt3.

The side chain of NAFION, a proton conductive membrane used as electrolyte in low-temperature fuel cells, is modeled with perfluorobutane sulfonic acid. Density functional theory is used to characterize structures and energetics of hydration of the model system interacting with a proton solvated with up to 24 water molecules and analyze interactions of some of these hydrated complexes with O(2) adsorbed on Pt(3). It is found that at least three water molecules are needed to ionize the sulfonic acid, and higher degrees of hydration induce the formation of cages where the water molecules are held together via complex hydrogen-bond networks. The interaction between the complex formed by the ionized acid and the hydrated proton, in contact with a bridge-adsorbed O(2)-Pt(3), promotes the protonation of the adsorbed O(2). Upon protonation, the O(2)-Pt(3) system evolves from hydrophobic to hydrophilic behavior, which may facilitate further interfacial contact.

Journal Article↗
PubMed2006

Performance of multiplicity-based energy correctors for molecules containing second-row elements.

We introduce a posteriori multiplicity-based corrections to ab initio energies in order to reproduce experimental atomization energies. This simple approach, as compared to the alternative ones to improve density functionals and standard correlated methods, requires less computational resources than higher levels of theory. We extend our approach to include molecules containing second-row elements. Molecules are taken from the Gaussian sets for which experimental values are known with errors of less than 1 kcal/mol. We postulate that inexpensive multiplicity-based corrections can account for effects that are not accounted because of the low level of theory of the method or because of the small basis used for the calculations.

Journal Article↗
PubMed2006

Energy correctors for accurate prediction of molecular energies.

Energy correctors are introduced for the calculation of molecular energies of compounds containing first row atoms (Li-F) to modify ab initio molecular orbital calculations of energies to better reproduce experimental results. Four additive correctors are introduced to compensate for the differences in the treatment of molecules with different spin multiplicities and multiplicative correctors are also calculated for the electronic and zero-point vibrational energies. These correctors, individually and collectively yield striking improvements in the atomization energies for several ab initio methods. We use as training set the first row subset of molecules from the G1 basis of molecules; when the correctors are applied to other molecules not included in the training set, selected from the G3 basis, similar improvements in the atomization energies are obtained. The special case of the B3PW91/cc-pVTZ yields an average error of 1.2 kcal/mol, which is already within a chemical accuracy and comparable to the Gaussian-n theories accuracy. The very inexpensive B3PW91/6-31G** yields an average error of 2.1 kcal/mol using the correctors. Methods considered unsuitable for energetics such as HF and LSDA yield corrected energies comparable to those obtained with the best highly correlated methods.

Journal Article↗
PubMed2006

Encoding information using molecular vibronics.

Signals carrying information are encoded in molecular vibrational waves (vibronics) rather than in electric currents as widely done in microelectronics. We demonstrate theoretically that signals can be transmitted along a long polypeptide molecule; the signal is modulated in a terahertz carrier corresponding to a frequency of an intrinsic vibrational mode of the backbone of the polypeptide, via amplitude and frequency modulations. The modulated carrier is coupled as a vibrational wave to the polypeptide at one end of the molecule and propagates for more than 168 angstroms towards the other end. Digital signal processing techniques are used to recover the modulated signals.

Computer Simulation↗
PubMed2005

Transmission of vibronic signals in molecular circuits.

It is proposed and demonstrated using molecular dynamics and digital signal processing techniques that molecular vibrations can be used to transport signals in molecular circuits, revealing that signals transmitted along polypeptide molecules by a frequency-modulated carrier in the terahertz domain consume only 0.2 eV to successfully transfer one information bit; this energy is several orders of magnitude smaller than the several thousands of electronvolts needed using electrons in present electronic devices.

Letter↗
PubMed2005

Electronic structure and electron transport characteristics of a cobalt complex.

The molecular and electronic structures and electron transport characteristics of a Co complex are investigated using first principles calculations. The Co complex belongs to the D(2d) point group, and its two ligands are perpendicular to each other. The central atom Co forms a distorted octahedron with six donor N atoms. In a low oxidation state, the bond length between Co and pyrrole nitrogen, 1.849 A, is much shorter than the distance between Co and pyridine nitrogen, 2.168 A, while, in a high oxidation state, the bond length differences between Co and pyrrole nitrogen, 1.814 A, and between Co and pyridine nitrogen, 1.990 A, are not as large as those in the Co2+ complex. The HOMO energy of the low oxidation state is very close to the Fermi level of bulk Au, allowing hole creation in the molecule. On the other hand, the LUMO energy of the high oxidation state is close to the Au Fermi level, allowing a low barrier for electron injection from the Au cathode to the molecule. These structural characteristics make the Co complex a good hole-conduction molecule. The density of states, transmission probability, and I-V characteristics are evaluated using the Green function approach.

Letter↗
PubMed2005

Vibrational study of a molecular device using molecular dynamics simulations.

A Potential scenario for the implementation of molecular electronic systems is introduced by applying digital signal processing techniques to results from classical molecular dynamics simulations of a molecular system interconnected by nanosize gold clusters. Under this new scenario, signals can be introduced, processed, and read through interactions with the internal vibrational modes of the small molecular unit. We use modulation operations intrinsically inherent to any molecular system as a concept proof. As an example of this type of analysis, we focus on the individual oscillations between C-H and C-C bonds and cluster-cluster displacements.

Carbon↗
PubMed2004

Clustering effects on discontinuous gold film NanoCells.

Reproducible negative differential resistance (NDR)-like switching behavior is observed in NanoCells. This behavior is attributed to the formation of filaments and clusters between the discontinuous gold films. Control experiments are performed by self-assembly of insulating molecules between the gold islands and conducting molecules on these islands. Additional control experiments are performed by removing the filaments and clusters between islands using a piranha bath. The results are consistent with theoretical predictions and extend the domain of molecular electronics based in organic molecules to include nanosized clusters as active units. This facilitates a scenario where synthetically accessible organic molecules, with defined characteristics, can be adjusted by metallic nanoclusters as an in situ fine-tuning element, able to compensate for the lack of addressing in the nanosize regime.

Electric Impedance↗
PubMed2003

A programmable molecular diode driven by charge-induced conformational changes.

The 3-nitro-2-(3'-nitro-2'-ethynylpyridine)-5-thiopyridine molecule shows charge-induced conformational switching and a rectifying behavior with a charge-induced controllable switching. This device can be used as a memory operated with an external field interacting with one of the rings local dipole. Alternatively, the molecule can be used as a nano-actuator controlling the rotation of the ring by charging the molecule with a bias voltage.

Journal Article↗
PubMed2002

Theoretical interpretation of switching in experiments with single molecules.

Identifying the factors that trigger current-switching behavior of single molecules establishes the means by which it may be possible to tailor these molecules to perform as electronic devices. We provide a theoretical interpretation of switching observed in recent experiments with single molecules using quantum chemistry tools. We conclude that the switching observed in the experiment is mostly due to conformational changes and that some charge changes cannot be observed in STM experiments.

Journal Article↗