RESUMEN
Two CO oxidation reactions (CO + O2 â CO2 + O and CO + O â CO2) were considered in the Eley-Rideal (ER) reaction mechanism. These oxidation processes on the W(111) surface and the W helical nanowire were investigated by the density functional theory (DFT) calculation. The stable adsorption sites of O2 and O as well as their adsorption energies were obtained first. In order to understand the catalytic properties of the W helical nanowire, the Fukui function and local density of state (LDOS) profiles were determined. The nudged elastic band (NEB) method was applied to locate transition states and minimum energy pathways (MEPs) of CO oxidation processes on the W helical nanowire and on the W(111) surface. In this study, we have demonstrated that the catalytic ability of the W helical nanowire is superior to that of the W(111) surface for CO oxidation.
RESUMEN
The adsorption and dissociation of H2O in Pd nanowire have been investigated by the density functional theory (DFT) studies. First, we construct Pd nanowire by basin-hopping method and use DFT calculation to find the ground state of Pd nanowire, and put the H2O molecular on different adsorption sites and the H2O molecule is found to preferentially absorb on a Top (T) site. The H2O molecule lies parallel to the Pd nanowire surface, while the O atom is bound at a Top site. We also calculate the partial density of state (PDOS) and election density difference. In addition, our calculated results demonstrate that the bonding between H2O and Pd nanowire is contributed by d orbitals of Pd nanowire and p orbitals of O atom. The nudged elastic band (NEB) method is applied to locate transition states and minimum energy pathways (MEP), and we discuss the dissociation behavior of the side-on H2O molecules on the top site of hexagonal and tetragonal planes, respectively.
RESUMEN
The mechanical properties of Ni-Ta crystallizationand binary bulk metallic glasses (BMG) were investigated for this study at the nanoscale. First, the Ta9Ni3 crystals are formed by space group, and structures with different ratios (Ta1Ni1, BTa8Ni4, BTa9Ni3, BTa7Ni5) were put into unit cell randomly. The optimizations of BMG structures are performed by Density functional theory (DFT) calculation to find the stable amorphous structures and corresponding energy. The FMM is utilized to obtain the suitable parameters of tight-binding potential bystable amorphous structures and corresponding energies. Finally, we employ molecular dynamics (MD) simulation to study mechanical properties of Ni/Ta crystallization and BMG, such as atomistic stress-strain, plastic and elastic deformation, and elastic modulus.
RESUMEN
The adsorption and dissociation properties of carbon monoxide (CO) molecule on tungsten W(n) (n = 10-15) nanoparticles have been investigated by density-functional theory (DFT) calculations. The lowest-energy structures for W(n) (n = 10-15) nanoparticles are found by the basin-hopping method and big-bang method with the modified tight-binding many-body potential. We calculated the corresponding adsorption energies, C-O bond lengths and dissociation barriers for adsorption of CO on nanoparticles. The electronic properties of CO on nanoparticles are studied by the analysis of density of state and charge density. The characteristic of CO on W(n) nanoparticles are also compared with that of W bulk.
RESUMEN
The studies of silica nanoclusters are of substantial interest for large potential in applications as diverse as photonics/optics, microelectronics and catalysis. In this study, we used the basing-hopping method with Buckingham potential to get the stable structures of silica nanoclusters ((SiO2)(n) = 1-13). The global minimum geometry of silica nanoclusters were determined by density functional theory calculation. We investigated the energy gap, binding energy and second order energy difference of nanoclusters to determine their structural stability with different sizes. We also calculate the second-order energy difference, binding energy to determine the magic number.
RESUMEN
The detailed structural variations of amorphous zinc oxide (ZnO) as well as wurtzite (B4) and zinc blende (B3) crystal structures during the temperature elevation process were observed by molecular dynamics simulation. The amorphous ZnO structure was first predicted through the simulated-annealing basin-hopping algorithm with the criterion to search for the least stable structure. The density and X-ray diffraction profiles of amorphous ZnO of the structure were in agreement with previous reports. The local structural transformation among different local structures and the recrystalline process of amorphous ZnO at higher temperatures are observed and can explain the structural transformation and recrystalline mechanism in a corresponding experiment [Bruncko et al., Thin Solid Films 520, 866-870 (2011)].
RESUMEN
The purpose of this study is to estimate the complete crosstalk effects, including the package and the pads on the surface acoustic wave (SAW) substrate. The coupling influence from the SAW pattern is investigated by the full-wave approach. In order to combine the electromagnetic effects with the surface acoustic wave response, a new approach based on finite difference time domain (FDTD) with equivalent current source method is applied. The resistive voltage source model is carefully used to simulate the situations of measurement by the vector network analyzer more accurately. Two kinds of patterns of one-port SAW resonators with the same package structure and interdigital transducer (IDT) design are studied. From the simulated electromagnetic field distributions over the substrate, it can be seen that, as the pattern on the SAW substrate becomes closer, more input energy will be coupled directly to the parallel pads by crosstalk without filtering. This will lead to more coupling loss and, therefore, the insertion loss becomes universally lower by about 2 to 3 dB. Furthermore, it can be observed that the coupling interference from the SAW pattern is more serious than from the package in this case. Verification with the measurement results shows that our method is able to obtain good agreement and can be used to observe the influence from the SAW pattern that can seriously affect the performance of the SAW device.