Wilson Agerico Dino

Potential energy of hydrogen atom motion on Pd(111) surface and in subsurface: A first principles calculation

We calculate the adiabatic potential energy for hydrogen atom motion on a Pd(111) surface and in a subsurface within the framework of the density functional theory in order to understand the diffusion mechanism of a hydrogen atom from the Pd(111) surface to the subsurface. According to the calculated adiabatic potential energy surface for the hydrogen atom motion up to the third atom layer, an effective diffusion path of the hydrogen atom into the Pd bulk starts from the fcc hollow site on the Pd(111) surface. Moreover, the diffusion path passes through the octahedral site between the first and the second Pd atom layers, the tetrahedral site beneath a Pd atom of the first layer or above the Pd atom of the third layer, and the octahedral site between the second and third layer.

Realizing a carbon-based hydrogen storage material

In response to the current need for an efficient, safe, and compact system for storing hydrogen in mobile applications, a scheme for maximizing and controlling hydrogen storage in graphite is proposed by modifying substrate reactivity through the exploitation of intrinsic vibrational modes in pristine and fully-hydrogenated graphite systems. Calculations within density functional theory suggest that infrared radiation of distinct frequencies can be used to independently induce graphite lattice restructuring and recrystallization for promoting hydrogen uptake and discharge, respectively. Effects of the initial attachment of hydrogen on graphite sheets are discussed, with computational results showing that additional hydrogen adsorption can proceed through easier reaction routes.

Quantum states of hydrogen atom motion on the Pd(111) surface and in the subsurface

We investigate the quantum states of hydrogen atom motion on Pd(111) surface and in its subsurface by calculating the wavefunctions and the eigenenergies for hydrogen atom motion within the framework of the variation method on an adiabatic potential energy surface (PES), obtained through first-principles calculations, for the hydrogen atom motion. The calculated results show that the ground-state wavefunction for the hydrogen atom motion localizes on the face-centered cubic (fcc) hollow site of the surface. The higher excited state wavefunctions are distributed between the first and second layers, and subsequently delocalized under the second atom layer. These suggest that an effective diffusion path of the hydrogen atom into the subsurface area passes through the fcc hollow site to the octahedral sites in the subsurface. Moreover, activation energies for diffusion of H and D atoms over the saddle point of the PES between the fcc hollow site and the first (second) octahedral site are estimated as 598 (882) meV and 646 (939) meV, respectively. Furthermore, the activation energies for diffusion of H and D atoms over the saddle point of the PES between the first (second) octahedral site and the fcc hollow site are estimated as 285 (483) meV and 323 (532) meV, respectively.

Diameter Dependent Magnetic and Electronic Properties of Single-Walled Carbon Nanotubes with Fe Nanowires

We investigate the electronic and magnetic properties of single-walled carbon nanotubes (SWNTs) filled with Fe nanowires, based on the spin-polarized density functional theory. We find that in the stable structure, the Fe-filled (3,3) and (5,0) SWNTs exhibit semiconducting properties, and the magnetic moment of Fe nanowires inside disappears. On the other hand, the Fe-filled (4,4), (5,5), (6,6) and (6,0) SWNTs, having larger radii, are metallic and exhibit ferromagnetic properties. The corresponding magnetic moment increases with increasing nanotube diameter.

Scattering and dissociative adsorption of H2 on the armchair and zigzag edges of graphite

We performed quantum dynamics calculations on the scattering and dissociative adsorption of hydrogen molecules incident on the armchair and zigzag edges of graphite layers, using relevant potential-energy surfaces (PESs) recently obtained by Dino et al. [e-J. Surf. Sci. Nanotech. 2, 77 (2003), and references therein]. By employing the coupled channel method to determine the reflection and sticking probabilities, we compared the hydrogen scattering and dissociative adsorption dynamics on the two graphite surfaces. Our findings show the different scattering behaviors of H2 for the armchair edge and for the zigzag edge, which enable the identification of an unknown graphite edge from its interaction with H2. The scattering on the zigzag edge is due to the highly curved region of the PES reaction path for H2 interacting with the zigzag edge, whereas the scattering for the armchair edge is caused by a potential barrier. The reflection probability initially decreases with increasing the kinetic energy in both c...

Vibrational properties of hydrogen atom adsorbed on Cu(111) and on Ir(111) surfaces

We investigate the quantum mechanical behavior, in particular, the vibrational properties, of H atoms adsorbed on metal surfaces. We carry out density functional theory–based calculations of the relevant potential energy curves (PECs) for the hydrogen on Cu(111) and Ir(111) systems and construct the adiabatic three-dimensional potential energy surfaces (PESs) based on the obtained PECs. The wave functions and the corresponding energies for the hydrogen motion on the PESs are calculated within the framework of the variation method. The results show that the H atom is adsorbed at the threehold hollow site of Cu(111) and it is strongly localized. On the other hand, on the Ir(111), the H atom is adsorbed at the top site and it exhibits delocalized features. Furthermore, our calculated energies for vibrationally excited hydrogen and deuterium adsorbed on Cu(111) and Ir(111) agree well with the corresponding recently observed high-resolution electron energy-loss spectroscopy loss peaks.

Magnetized/charged MgH2-based hydrogen storage materials

We propose two methods to facilitate the Mg–H bond cleavage of magnesium hydride MgH2. We found via density functional calculations that Mn (or Fe), when inserted between two MgH2, exhibits a much higher catalytic activity than the other 3d transition metal elements because of the induced spin polarization of the MgH2. We also found that an ionized MgH2 (MgH2+) has considerably softer Mg–H bonds. We can thus significantly reduce the H2 desorption temperatures from MgH2 to practical levels, ∼400K, by forming an alloy hydride with Mn (or Fe), and/or ionizing the MgH2.

Reactive Ion Etching of NiFe Thin Films from First-Principles Study: A Case Study

We propose a reactive ion etching (RIE) process design from first-principles calculations for implementation to NiFe thin-film etching. We consider the interaction between the magnetic metal surface NiFe and various gases. We found that the gases CO/NH3, or CH3OH/O2(/NH3,H2) enable the NiFe surface to be etched.

Cyclohexane dehydrogenation catalyst design based on spin polarization effects

We investigate and discuss spin polarization effects on cyclohexane (C6H12) dehydrogenation using a Ni atom as a test catalyst, by performing total energy calculations based on the density functional theory (DFT). We compare the results with those of the well known catalyst Pt. We consider the process where cyclohexane approaches a transition metal M (M: Ni and Pt), and determine the reaction paths from the calculated potential energy surfaces (PESs) for singlet cyclohexane/M and triplet cyclohexane/Ni systems. Unlike the singlet cyclohexane/Ni, no energy is required to separate cyclohexyl intermediate (C6H11) from the H–Ni system for the triplet cyclohexane/Ni. Our results suggest that the catalytic reactivity of spin-polarized Ni becomes close to that of Pt, which is considered to be, up to now, the best catalyst for cyclohexane dehydrogenation.

Polybutylene terephthalate on metals: a density functional theory and cluster models investigation

The strength of adhesion of polybutylene terephthalate (PBT) on aluminium is investigated using density functional theory-based energy calculations. The aluminium atom is connected to a PBT monomer at different orientations, and total energies are calculated and compared to determine the most stable orientation. The binding is strongest when the Al is oriented at 180° to the ester group of the monomer. Using this orientation as a basis, PBT adhesion on Ti, Ag, and Au is also investigated.