Dynamical properties of Au from tight-binding molecular-dynamics simulations

We studied the dynamical properties of Au using our previously developed tight-binding method. Phonon-dispersion and density-of-states curves at T=0 K were determined by computing the dynamical-matrix using a supercell approach. In addition, we performed molecular-dynamics simulations at various temperatures to obtain the temperature dependence of the lattice constant and of the atomic mean-square-displacement, as well as the phonon density-of-states and phonon-dispersion curves at finite temperature. We further tested the transferability of the model to different atomic environments by simulating liquid gold. Whenever possible we compared these results to experimental values.Comment: 7 pages, 9 encapsulated Postscript figures, submitted to Physical Review

Thermal formation of carbynes

We simulate the formation of $sp$ carbon chains (carbynes) by thermal decomposition of $sp^2$ carbon heated by a hot discharge plasma, by means of tight-binding molecular dynamics. We obtain and analyze the total quantity of carbynes and their length distribution as a function of temperature and density

Photo-induced volume changes in selenium. Tight-binding molecular dynamics study

Tight-binding molecular dynamics simulations of photo-excitations in small Se clusters (isolated Se$_8$ ring and helical Se chain) and glassy Se networks (containing 162 atoms) were carried out in order to analyse the photo induced instability inside the amorphous selenium. In the cluster systems after taking an electron from the highest occupied molecular orbital to the lowest unoccupied molecular orbital a bond breaking occurs. In the glassy networks photoinduced volume expansion was observed and at the same time the number of coordination defects changed significantly due to illumination

Factors Responsible for the Stability and the Existence of a Clean Energy Gap of a Silicon Nanocluster

We present a critical theoretical study of electronic properties of silicon nanoclusters, in particular the roles played by symmetry, relaxation, and hydrogen passivation on the the stability, the gap states and the energy gap of the system using the order-N [O(N)] non-orthogonal tight-binding molecular dynamics and the local analysis of electronic structure.Comment: 26 pages including figure

Nonorthogonal Tight-Binding Molecular Dynamics for Si(1-x)Ge(x) Alloys

We present a theoretical study of Si(1-x)Ge(x) alloys based on tight-binding molecular dynamics (TBMD) calculations. First, we introduce a new set of nonorthogonal tight-binding parameters for silicon and germanium based on the previous work by Menon and Subbaswamy [Phys. Rev. B 55, 9231 (1997); J. Phys: Condens. Matter 10, 10991 (1998)]. We then apply the method to structural analyses of Si(1-x)Ge(x) alloys. The equilibrium volume and atomic structure for a given x are obtained by the TBMD method. We also calculate the bulk modulus B, elastic constants C(11), C(12) and C(44) as a function of x. The results show that the moduli vary monotonically, but nonlinearly, between the values of Si crystal and Ge crystal. The validity of the results is also discussed

Tight-binding molecular-dynamics studies of defects and disorder in covalently-bonded materials

Tight-binding (TB) molecular dynamics (MD) has emerged as a powerful method for investigating the atomic-scale structure of materials --- in particular the interplay between structural and electronic properties --- bridging the gap between empirical methods which, while fast and efficient, lack transferability, and ab initio approaches which, because of excessive computational workload, suffer from limitations in size and run times. In this short review article, we examine several recent applications of TBMD in the area of defects in covalently-bonded semiconductors and the amorphous phases of these materials.Comment: Invited review article for Comput. Mater. Sci. (38 pages incl. 18 fig.

Silicon self-diffusion constants by tight-binding molecular dynamics

The thermodynamic integration method has been incorporated into the tight-binding molecular-dynamics scheme to compute formation free energies of native point defects in bulk silicon. By combining previous simulated diffusivity data with present free-energy estimates, we present a thorough quantum-mechanical picture of self-diffusion in silicon that is both consistent with the state-of-the-art experimental data and able to predict separately the vacancy and self-interstitial contributions.Peer reviewe