Papers by Keyword: Tight-Binding

Abstract: The computer simulation method was used to examine condensation of 90124 Cu and Au atoms from the gas phase. To analyze the synthesis processes, there were selected chemical compositions Cu₃Au, Cu-Au, Cu₉₀Au₁₀ and Cu₆₀Au₄₀ being cooled with liquid nitrogen during the condensation. The undertaken simulation showed that the increase in the percentage of gold atoms in the initial couple decreases the number of clusters of a relatively large size. Moreover, the analysis of the external view and the structure of Cu-Au nanoparticles of various chemical composition allowed us to conclude that a large number of binary nanoparticles were of an icosahedral structure.

Abstract: A many-body interatomic potential for metallic nanowires within the second-moment approximation of the tight-binding model (the Cleri-Rosato potential) was employed to carry out three dimensional molecular dynamics simulations. Molecular dynamics simulation results for metallic nanowires at various temperature are presented. The stress–time and stress length curves for nanowires are simulated. The breaking and yield stress of nanowires are dependent on the Volume and temperature. The necking, Plastic deformation, slipping domain, twins, clusters, microspores and break-up phenomena of nanowire are demonstrated. Stress decreases with increasing nanowire volume and temperature. The final breaking position occurs at the central part of the nanowire when it is short, as the nanowire length increases the breaking position gradually shifts to the ends.

Abstract: In this thesis, aperiodic genomic DNA have weak charge transfer; the transmission coefficient of DNA with short period sequence does not seem to depend on the length, yet differently, the transmission pattern of aperiodic genomic DNA sequences strongly depends on the strand length. As the number of corresponding bases increases, fewer states will present good transmission ability, because aperiodic increasing bases make more backscattering; at low temperature, the transmission spectrum presents a higher number of transmitting states, due to a breaking of level degeneracy. At higher temperature, the number of transmitting states decreases; Small intrastrand hopping integral does not seem to diminish the transmission coefficient, but shrinks the location in the three-dimension figure. And the distribution of energy is concentrated.

Abstract: We have studied the equation of states and vibrational properties of FeO using DFT based plane-wave pseudopotential (PW-DFT) within the generalized gradient approximation. The calculated cohesive properties at ambient condition, namely, lattice constant (a₀), bulk modulus (B₀) and its first pressure derivative (), are reported for B1-phase of FeO, in agreement with previous experimental and other theoretical results. A linear-response approach to the density functional theory was used to derive the phonon frequencies and phonon density of state (p-dos). Further, in order to calculate both static and dynamic equations of states, nearest-neighbour second-moment tight-binding energy model (TB-SMA) was used. Parameters of the present TB-SMA model were determined by the present ab initio pseudopotential calculations. It is found that the present simple TB-SMA scheme is able to mimic shock Hugoniot for such oxides correctly.

Abstract: The effects on the electronic band structure of hydrogenated cubic silicon carbide (-SiC) nanowires of changes in the diameter and morphology are studied using a semiempirical sp3s* tight-binding approach applied to a supercell model. The results of the calculation of the electronic band structure and electronic density of states obtained are compared with those calculated by density functional theory within local density approximation only for the bulk of -SiC. As boundary conditions, we passivated all the Si and C dangling bonds with hydrogen atoms. The results show that although surface morphology modifies the band gap, the change is more systematic with the thickness variation. The energy band gap increases with decreasing diameter in all cases because of quantum confinement, but the scaling is dependent on the morphology (cross-section) of the -SiC nanowires. Finally, the calculations show a consistent asymptotical behavior to the crystalline limit when the width of the wires enlarges.

Abstract: In this work, the effects of the diameter and morphology on the electronic band structure of hydrogenated cubic silicon carbide (b-SiC) nanowires is studied by using a semiempirical sp3s* tight-binding (TB) approach applied to the supercell model, where the Si- and C-dangling bonds on the surface are passivated by hydrogen atoms. Moreover, TB results (for the bulk) are compared with density functional calculations in the local density approximation. The results show that though surface morphology modifies the band gap, the change is more systematic with the thickness variation. As expected, hydrogen saturation induces a broadening of the band gap energy because of the quantum confinement effect.