Atomistic simulations of nanometer size metal clusters
Abstract
The atomic structure, melting behavior, and elastic properties of nanometer-size metal clusters are investigated through atomistic simulations. The lowest energy atomic structure of a cluster as a function of cluster size is explored both for various metals described by the embedded atom method (EAM) interatomic potential and for inert gases described by the pair-wise Lennard-Jones (LJ) potential. We find that the preferred structure for large clusters is a single FCC crystal, the same structure that is exhibited in the bulk. Small clusters, in contrast prefer a multiply twinned icosahedral structure. The exact size at which the transition to a single FCC crystal occurs is dependent on the material. There appears to be an inverse correlation between the transition size and the non-dimensionalized elastic constant C$\sbsp{12}{*}$ of the bulk material. The melting behavior of clusters with up to 586 atoms is examined. Different interaction potentials, viz., Lennard-Jones, gold (EAM), and nickel (EAM) are studied. The melting temperatures obtained by means of molecular dynamics are correlated with a model obtained from classical thermodynamics. A plot of the ratio of the cluster melting over the bulk melting temperature versus the reciprocal of the number of atoms raised to the one third power yields a "universal" curve for the three interaction potentials. The elastic deformation of nanometer scale gold (EAM) clusters is studied. The elastic compression and harmonic vibration of a series of truncated octahedral clusters having FCC symmetry (N = 38, 201, 586, 1289, 2406) are simulated by molecular dynamics calculations. The yield stress at 0 K for these clusters is also calculated and correlated with cluster size. It is found that the simulation results, both for static compression at 0 K and for harmonic vibration, can be modeled in terms of a continuum elastic constant analogous to the bulk elastic modulus.
Degree
Ph.D.
Advisors
Talbot, Purdue University.
Subject Area
Chemical engineering
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