Diffusion of the Cu monomer and dimer on Ag(111): Molecular dynamics simulations and density functional theory calculations

We present results of molecular dynamics (MD) simulations and density functional theory (DFT) calculations of the diffusion of Cu adatom and dimer on Ag(111). We have used potentials generated by the embedded-atom method for the MD simulations and pseudopotentials derived from the projected-augmented-wave method for the DFT calculations. The MD simulations (at three different temperatures: 300, 500, and 700 K) show that the diffusivity has an Arrhenius behavior. The effective energy barriers obtained from the Arrhenius plots are in excellent agreement with those extracted from scanning tunneling microscopy experiments. While the diffusion barrier for Cu monomers on Ag(111) is higher than that reported (both in experiment and theory) for Cu(111), the reverse holds for dimers [which, for Cu(111), has so far only been theoretically assessed]. In comparing our MD result with those for Cu islets on Cu(111), we conclude that the higher barriers for Cu monomers on Ag(111) results from the comparatively large Ag-Ag bond length, whereas for Cu dimers on Ag(111) the diffusivity is taken over and boosted by the competition in optimization of the Cu-Cu dimer bond and the five nearest-neighbor Cu-Ag bonds. Our DFT calculations confirm the relatively large barriers for the Cu monomer on Ag(111)-69 and 75 meV-compared to those on Cu(111) and hint a rationale for them. In the case of the Cu dimer, the relatively long Ag-Ag bond length makes available a diffusion route whose highest relevant energy barrier is only 72 meV and which is not favorable on Cu(111). This process, together with another involving an energy barrier of 83 meV, establishes the possibility of low-barrier intercell diffusion by purely zigzag mechanisms

Nanoscale relaxation near twin-interfaces of palladium and platinum

730-736Molecular dynamics simulation technique with many-body and semi-empirical potentials, based on the embedded atom method is employed to calculate some low index (111), (311), (211) and (210) twin-boundaries at various temperatures. Multilayer relaxation near these twin interfaces for Pd and Pt has also been investigated. For all interfaces except (111), due to high atomic density of (111) plane, considerable relaxation is found on both sides of the interfaces with the same magnitude. The interlayer relaxation near (311) and (211) interfaces is in oscillatory order while near (210) interface is of random nature. Maximum contraction 84.16% and 83.18% for 2nd interplanar spacing is found for Pd and Pt, respectively. This shows partial coalescence of the planes near (211) twin interface. Furthermore, percentage registry relaxation is calculated for the planes in the vicinity near the interfaces

Correlation between structural, electronic, and optical response of Ga-doped AlSb for optoelectronic applications: a first principle study

Density functional theory is used to examine structural, electronic, and optical properties of Al1−xGaxSb by employing the full potential linear augmented plane wave method. Structure parameters as lattice constants, bulk modulus, pressure derivatives, ground-state energy, and volume optimization are employed by generalizing gradient approximation (GGA-PBE). A remarkable deviation of lattice constant and Bulk modulus is observed by adding the concentration of Ga atoms in AlSb. Electronic properties like band structure and density of states are calculated by GGA-PBE with the addition of the Tran–Blaha-modified Becke–Johnson (TB–mBJ) approach. The calculated results demonstrate that the binary compound AlSb shows an indirect (Γ–X) bandgap and is optically inactive. By increasing Ga concentration in AlSb at varying percentage, bandgap transforms from indirect to direct (Γ–Γ) and the material becomes optically active. There is a marked change in optical behavior in dielectric constant, optical conductivity, reflectivity, refractive index, and absorption coefficient, and energy loss by adding Ga concentration in AlSb. Obtained results are analyzed with experimental data and employed as a gateway to suggest that material is the best candidate for optoelectronic applications