Tight-binding Molecular Dynamics Approach Research Articles

Mechanisms and kinetics of initial pyrolysis and combustion reactions of 1,1-diamino-2,2-dinitroethylene from density functional tight-binding molecular dynamics simulations

The density functional tight-binding molecular dynamics approach was used to study the mechanisms and kinetics of initial pyrolysis and combustion reactions of isolated and multi-molecular FOX-7. Based on the thermal cleavage of bridge bonds, the pyrolysis process of FOX-7 can be divided into three stages. However, the combustion process can be divided into five decomposition stages, which is much more complex than the pyrolysis reactions. The vibrations in the mean temperature contain nodes signifying the formation of new products and thereby the transitions between the various stages in the pyrolysis and combustion processes. Activation energy and pre-exponential factor for the pyrolysis and combustion reactions of FOX-7 were obtained from the kinetic analysis. It is found that the activation energy of its pyrolysis and combustion reactions are very low, making both take place fast. Our simulations provide the first atomic-level look at the full dynamics of the complicated pyrolysis and combustion process of FOX-7.

Local order in undercooled liquid metals: A tight binding molecular dynamics approach

We use constant (zero) pressure molecular dynamics based on a semi-empirical tight binding model to simulate the structures of liquid Ni, Cu, Pd and Au in the stable and undercooled states. We compare our data with the available experiments (neutron scattering for Ni, EXAFS for Pd). We analyze the structure in terms of Voronoi polyhedra and use the neighbors defined by this analysis to perform a Common Neighbors Analysis. We show that a small but significant difference in the number of bonds with five common neighbors exists between undercooled Ni and the other elements. We question the possible experimental observation of such a difference and its relevance to the issue of the existence of an icosahedral short range order in the liquid.

Fragmentation of C60, C70 by tight-binding molecular-dynamics approach

We have studied fragmentation of fullerenes using tight-binding molecular dynamics approach. The C 60 and C 70 molecules form floppy phase with fluctuations ± 0.4 Å at 3000 K but do not disintegrate. We observe that a window is opened at high temperature when a bond between pentagon and hexagon is broken, forming 9 membered rings, which may play an important role for the formation of endohedral fullerene compounds. Higher membered rings such as 13 and 16 membered rings are also found, forming larger windows. The C 2 , C 4 , and C 5 are formed during the disintegration. Both form linked chains after complete disintegration at 5000 K. Possible explanation for the formation of fullerenes is given. We also find that the latent heat of C 60 and C 70 are 1.65 and 1.29 eV, respectively, larger than that of graphite (1.08 eV).

Structural, electronic, and vibrational properties of liquid and amorphous silicon: Tight-binding molecular-dynamics approach.

Liquid and amorphous silicon networks are generated by a tight-binding molecular-dynamics method. The structural, electronic, and vibrational properties are calculated. The generated amorphous silicon networks are mostly fourfold coordinated with dangling bonds (3.2%) and floating bonds (12.5%). The calculated results are in excellent agreements with previous ab initio results. The results are further compared to the experimental results and those of other classical models.

New Approaches to Molecular Dynamics Simulations of a-Si:H

ABSTRACTA new tight-binding molecular dynamics approach for Si-H systems is developed using the valence orbitale of Si and H for calculation of atomic forces. Previous tight-binding models are not able to describe formation energies of different charge states of H in c-Si and new physics is introduced in our model to describe both effects of charge transfer and varying atomic environments. The Si-H Model was developed by fitting to silane, and ensuring that the formation energies of different charge states of H in c-Si were correctly described. This new model also describes well vibrational properties of SiHn configurations, and the structural and electronic properties of a-Si:H Models. The new molecular dynamics utilizes quantum mechanical forces, incorporating important electronic effects, and is robust enough to simulate hundreds of atoms as would be needed in realistic a-Si:H systems.