Melting as a String-Mediated Phase Transition

We present a theory of the melting of elemental solids as a dislocation-mediated phase transition. We model dislocations near melt as non-interacting closed strings on a lattice. In this framework we derive simple expressions for the melting temperature and latent heat of fusion that depend on the dislocation density at melt. We use experimental data for more than half the elements in the Periodic Table to determine the dislocation density from both relations. Melting temperatures yield a dislocation density of (0.61\pm 0.20) b^{-2}, in good agreement with the density obtained from latent heats, (0.66\pm 0.11) b^{-2}, where b is the length of the smallest perfect-dislocation Burgers vector. Melting corresponds to the situation where, on average, half of the atoms are within a dislocation core.Comment: 18 pages, LaTeX, 3 eps figures, to appear in Phys. Rev.

Liquid antiferromagnets in two dimensions

It is shown that, for proper symmetry of the parent lattice, antiferromagnetic order can survive in two-dimensional liquid crystals and even isotropic liquids of point-like particles, in contradiction to what common sense might suggest. We discuss the requirements for antiferromagnetic order in the absence of translational and/or orientational lattice order. One example is the honeycomb lattice, which upon melting can form a liquid crystal with quasi-long-range orientational and antiferromagnetic order but short-range translational order. The critical properties of such systems are discussed. Finally, we draw conjectures for the three-dimensional case.Comment: 4 pages RevTeX, 4 figures include

Dislocation-Mediated Melting: The One-Component Plasma Limit

The melting parameter $\Gamma_m$ of a classical one-component plasma is estimated using a relation between melting temperature, density, shear modulus, and crystal coordination number that follows from our model of dislocation-mediated melting. We obtain $\Gamma_m=172\pm 35,$ in good agreement with the results of numerous Monte-Carlo calculations.Comment: 8 pages, LaTe

MOLECULAR DYNAMICS CALCULATIONS OF MICROCLUSTER PROPERTES

Les propriétés structurales et thermodynamiques des microclusters à 2 et 3 dimensions ont été étudiées par la technique de la dynamique moléculaire. Cette technique donne en principe pour chaque taille de cluster la configuration atomique de plus basse énergie libre. La fonction d'état des différents microclusters a été calculée en se servant d'une fonction de potentiel de paire de type Lennard-Jones tronquée. On a étudié le processus de fusion ainsi que certaines propriétés telles que la température de fusion, la chaleur latente de fusion et les phénomènes de préfusion qui se sont révélés être dépendants de la taille du cluster aussi bien que de la structure de la phase solide.The structural and thermodynamic properties of microclusters in two and three dimensions have been investigated by means of the molecular dynamics technique. This technique in principle produces the atomic configuration of lowest free energy for any given cluster size. The caloric equation of state for the different microclusters were calculated using a truncated Lennard-Jones pair potential. The nature of the melting transition was investigated and a number of properties, such as melting temperature, latent heat of melting, and premelting phenomena, were found to vary with cluster size, as well as with the structure of the solid phase