The organic functional group effect on the electronic structure of graphene nano-ribbon: A first-principles study

We report a first-principles study of the electronic structure of functionalized graphene nano-ribbon (aGNRs-f) by organic functional group (CH2C6H5) and find that CH2C6H5 functionalized group does not produce any electronic states in the gap and the band gap is direct. By changing both the density of the organic functional group and the width of the aGNRs-f, a band gap tuning exhibits a fine three family behavior through the side effect. Meanwhile, the carriers at conduction band minimum and valence band maximum are located in both CH2C6H5 and aGNR regions when the density of the CH2C6H5 is big; while they distribute dominantly in aGNR conversely. The band gap modulation effects make the aGNRs-f good candidates with high quantum efficiency and much more wavelength choices range from 750 to 93924 nm both for lasers, light emitting diodes and photo detectors due to the direct band gap and small carrier effective masses.Comment: 20 pages, 5 figure

Early Stage of Oxidation on Titanium Surface by Reactive Molecular Dynamics Simulation

Understanding of metal oxidation is very critical to corrosion control, catalysis synthesis, and advanced materials engineering. Metal oxidation is a very complex phenomenon, with many different processes which are coupled and involved from the onset of reaction. In this work, the initial stage of oxidation on titanium surface was investigated in atomic scale by molecular dynamics (MD) simulations using a reactive force field (ReaxFF). We show that oxygen transport is the dominant process during the initial oxidation. Our simulation also demonstrate that a compressive stress was generated in the oxide layer which blocked the oxygen transport perpendicular to the Titanium (0001) surface and further prevented oxidation in the deeper layers. The mechanism of initial oxidation observed in this work can be also applicable to other self-limiting oxidation

Tight-Binding Molecular-Dynamics Study of Defects in Silicon

A tight-binding molecular-dynamics scheme is shown to have the efficiency and accuracy to study complex Si systems. We first establish the reliability of the scheme by showing that simulation results of liquid Si are nearly identical to ab initio (Car-Parrinello) results. The ability of the method to study complex systems is demonstrated by calculating defect formation energies and atomic configurations around vacancies and self-interstitials, with simulation unit cells of up to 512 atoms. The calculated formation energies compare well with first-principles results

Material Research with Tight-Binding Molecular Dynamics

Tight-binding molecular dynamics has recently emerged as a useful method for studying the structural, dynamical and electronic properties of realistic systems. In this article, we briefly review some recent achievements of the tight-binding molecular dynamics method and discuss some opportunities for future development

Overtone Phonon States and the Sharp Two-Phonon Raman Peak in Diamond

Phonon dispersions near the Brillouin zone center and the two-phonon overtone states at the high frequency region in diamond are studied with a tight-binding potential model previously developed. We found that the uppermost phonon branch has its minimum frequency at the zone center leading to a peak in the two-phonon overtone density-of-states at frequency bigger than twice of the one-phonon Raman frequency. The frequency shift and line shape of the two-phonon peak are compared with the experimental data

Structure and Dynamics of C₆₀ and C₇₀ from Tight-Binding Molecular Dynamics

Structural and vibrational properties of C60 and C70 fullerenes are studied by molecular dynamics using a recently developed tight-binding potential model. It is shown that this tight-binding molecular-dynamics scheme has accuracy comparable to ab initio techniques and is very efficient for studying the finite temperature properties of fullerenes

Empirical Tight-Binding Force Model for Molecular-Dynamics Simulation of Si

A scheme of molecular-dynamics simulation using the empirical tight-binding force model is proposed. The scheme allows the interatomic interactions involved in the molecular dynamics to be determined by first-principles total-energy and electronic-structure calculations without resorting to fitting experimental data. For a first application of the scheme we show that a very simple nearest-neighbor two-center empirical tight-binding force model is able to stabilize the diamond structure of Si within a reasonable temperature range. We also show that the scheme makes possible the quantitative calculation of the temperature dependence of various anharmonic effects such as lattice thermal expansion, temperature-dependent phonon linewidths, and phonon frequency shifts

Tight-Binding Molecular-Dynamics Study of Phonon Anharmonic Effects in Silicon and Diamond

The anharmonic effects on phonons in silicon and diamond have been studied by molecular-dynamics simulations using an empirical tight-binding Hamiltonian. One-phonon spectral intensities of the zone-center and zone-boundary (X) modes have been calculated through the Fourier transform of the velocity-velocity correlation functions. This scheme allows a quantitative and nonperturbative study of phonon frequency shift and phonon linewidth as a function of temperature. The results obtained are in good agreement with experimental data

Tight-Binding Molecular-Dynamics Study of Amorphous Carbon

The structural and electronic properties of amorphous carbon are studied with tight-binding molecular-dynamics simulations. An amorphous carbon structure with 216 atoms obtained from our simulation gives a structure factor S(Q) in very good agreement with the results of neutron scattering from a sputtered a-C sample. We found that the amorphous structure consists of graphitelike fragments embedded in a matrix of both twofold and fourfold coordinated atoms. We also found a small pseudogap in the electronic density of states at the Fermi level

Tight-Binding Molecular-Dynamics Study of Liquid Si

We have carried out molecular-dynamics simulation of liquid Si using the tight-binding Hamiltonian proposed by Goodwin, Skinner and Pettifor. The simulation results on the structural and dynamical properties (radial and angular distribution functions, the electronic density-of-states, and the diffusion constant) are presented and compared with results from classical-potential simulation and ab initio molecular dynamics (Car-Parrinello method)