A valence bond study of the activation of methyl halides bonds by electric fields

In the present work, the activation of methyl halides bonds under experience of an external electric field (EEF) is explained from the Valence Bond theory perspective. The dissociation mechanism of C–X bonds (X [Formula: see text] Cl, Br, I) influenced by a homogeneous and a heterogeneous field placed parallel to the bond axis is presented. For all examples, an increase in the electric field strength have similar consequences: (i) the decrease of the energy depth along the dissociation path, (ii) an increase of the equilibrium interatomic distance (at high EEFs), and (iii) the transition from a homolytic to a heterolytic dissociation after some field magnitude. These general behaviors are explained through the curve crossing between the ionic and the covalent structure at some field strength.

Dissociation path competition of radiolysis ionization-induced molecule damage under electron beam illumination

Molecule damage under TEM electron beam illumination is studied using a systematical ab initio method. Three main dissociation paths are revealed which explains the experimentally observed mass spectra of the dissociation fragments of the C2H6O2+.

Influences of Fe Doping on the Electronic Structure of Mg(0001) Surface and Hydrogenation Mechanism in Fe-Doped Mg(0001) Surface

First-principles calculations within the density functional theory (DFT) have been carried out to study the interaction of hydrogen molecule with Fe-doped Mg (0001) surfaces. First we have calculated the stability of the Fe atom on the Mg surface, On the basis of the energetic criteria, Fe atom prefer to substitute one of the Mg atoms from the second layer. In the second step, we have studied the interaction between hydrogen molecule and the Fe-doped Mg (0001) surface. The results show that for Fe atoms doped Mg (0001) surface in the second layer, enhances the chemisorption interaction between H2molecule and Fe atom, but also benefits H atom diffusion into Mg bulk with relatively more diffusion paths compared with that of clean Mg surface. Charge density difference plots provided some ideas about why certain alloying elements on the surface reduce the energy barrier of H2molecule dissociation on Fe-doped Mg (0001) surface. We can see that Fe as catalyst for the hydrogenation/dehydrogenation of Mg alloy samples and provide more dissociation path for H2molecule and diffusion paths for H atom, The present results not only beneficial for clarify the experimentally observed fast hydrogenation kinetics for Fe-capped Mg materials but also help to design new types of hydrogen storage materials for practical applications in the auto industry.

ADSORPTION AND DISSOCIATION OF PH3 ON SiGe(100) (2 × 1) SURFACE

The most stable structures for the adsorption and dissociation of phosphine ( PH 3) on SiGe (100) (2 × 1) surface have been investigated by relative total energy calculations based on density functional theory. According to the optimization calculations, PH 3 is adsorbed on the Si (down) and Ge (down) site of the Ge – Si and Ge – Ge dimers on SiGe surface, respectively. The PH 2 and H products have been found to be thermodynamically favored in the dissociation path of PH 3 on SiGe surface when the system is thermally activated. Although PH 3 is adsorbed on the Ge – Ge and Ge – Si dimers directly, it dissociates on the SiGe surface by passing through a transition state. The asymmetric Ge – Si and Ge – Ge dimers on SiGe surface are found to be approximately symmetric after the dissociation of PH 3 on the surface. The present work has showed that PH 2 prefers to be adsorbed on Ge site of the Ge – Si dimer. Therefore, the adsorption of PH 2 on Ge site of the Ge – Si dimer, while PH 3 being dissociated on the Si site, has indicated the migration of PH 2 on SiGe surface.

DISSOCIATION OF PH3 AND AsH3 ON Ge(100)(2x1) SURFACE

The most stable structures for the dissociation of phosphine and arsine on Ge (100)(2x1) surface have been investigated by relative total energy calculations based on Density Functional Theory. It has been found that the thermodynamically preferred structures in the dissociation path of phosphine and arsine are the same; PH 2 and AsH 2 products prefer to be on a single Ge dimer bond, but PH and AsH prefer to be between the adjacent Ge dimers. According to the optimization calculations, the dissociation path started with the adsorption of PH 3( AsH 3) on the electron deficient side of the Ge dimer bond is ended with the formation of P – P ( As – As ) dimers parallel to the dimers of Ge .

Ab Initio Study of Electronic and Geometric Structures of Metal/Ceramic Heterophase Boundaries

ABSTRACTThe adhesion geometries of coherent cube-on-cube interfaces between spinel (MgAl2O4) and the two metals Al and Ag were determined by density functional band structure calculations in the local density approximation (LDA). For Al/MgAl2O4, for which experimental data are available, the calculated optimum interface geometry is in excellent agreement with HRTEM measurements (distance dint: 1.90 Å calc., 1.90±0.04 Å exp.).The work of adhesion Wad is calculated for three different high-symmetry translation states between an Al-0 terminated (001) surface of the spinel and the (001) surface of each of the metals. The binding energy curves display a distinct optimum for the adhesion of aluminum atoms on top of the spinel oxygen ions at a Wad value of 2.4 J/m2. For silver several adsorption sites are isoenergetic at 1.1 J/m2 and the intersections of the Wad (dint) curves indicate a low-energy dissociation path. A further analysis of the electronic structure in the Al/MgAl2O4 system reveals the charge redistribution in the metal towards the oxygen ions as the main contribution to bonding. On the contrary, polarization of the metal film is the major effect observed on the adhesion of Ag to the spinel substrate.