Molecular dynamics simulations, with the interaction between atoms described by a modified analytic embedded atom method, have been performed to obtain the atomic-scale details of isothermal melting in nanocrystalline Ag and crystallization from supercooled liquid. The radial distribution function and common neighbor analysis provide a visible scenario of structural evolution in the process of phase transition. The results indicate that melting at a fixed temperature in nanocrystalline materials is a continuous process, which originates from the grain boundary network. With the melting developing, the characteristic bond pairs 555 , 433 , and 544 , existing in liquid or liquidlike phase, increase approximately linearly till completely melted. The crystallization from supercooled liquid is characterized by three characteristic stages: nucleation, rapid growth of nucleus, and slow structural relaxation. The homogeneous nucleation occurs at a larger supercooling temperature, which has an important effect on the process of crystallization and the subsequent crystalline texture. The kinetics of transition from liquid to solid is well described by the Johnson-Mehl-Avrami equation.

Using molecular dynamics simulations with an analytical embedded-atom method (MAEAM) model, the diffusion behavior of helium atoms at two Σ=5 symmetric grain boundaries of Ni was investigated in the present paper. The simulations demonstrate that the interstitial helium atoms are stable at the grain boundaries. Helium atoms in Ni lattices could diffuse easily to the grain boundary and precipitate into a cluster, which confirmed the fact that helium atoms could nucleate and grow up into bubbles at the grain boundaries. The diffusion activation energy of interstitial helium atom at grain boundaries was also determined.

In the present paper, the surface and size effects on the alloying ability and phase stability of immiscible alloy nanoparticles have been studied with calculating the heats of formation of Au-Pt alloy nanoparticles from the single element nanoparticles of their constituents (Au and Pt) with a simple thermodynamic model and an analytic embedded atom method. The results indicated that, besides the similar compositional dependence of heat of formation as in bulk alloys, the heat of formation of alloy nanoparticles exhibits notable size-dependence, and there exists a competition between size effect and compositional effect on the heat of formation of immiscible system. Contrary to the positive heat of formation for bulkimmiscible alloys, a negative heat of formation may be obtained for the alloy nanoparticles with a small size or dilute solute component, which implies a promotion of the alloying ability and phase stability of immiscible system on a nanoscale. The surface segregation results in an extension of the size range of particles with a negative heat of formation. The molecular dynamics simulations have indicated that the structurally and compositionally homogeneous Au Pt nanoparticles tend to form a core-shell structure with temperature increasing.

The surface premelting, melting behavior, melting competition, and structural transition of shell-closed icosahedral ICO and cuboctahedral CUB nickel clusters with atoms from 309 to 2057 were discussed extensively by using quantitative caloric curves based on the modified analytic embedded atom method and molecular dynamics, qualitative three-dimensional structural visualization of symmetric truncation, and the radial number distribution function. These studies reveal that smaller clusters melt at lower temperatures and a solid-to-solid structural transition occurs from CUB to ICO structure during melting process. The shell-closed ICO clusters could only be preferred until 923 atoms at temperatures no higher than 1380 K, which is in agreement with the experiments. The melting temperature of larger clusters would depend on their starting structures, which can be attributed to surface premelting.

Analytic embedded-atom method (EAM) interatomic potentials for body-centered cubic (bcc) transition metals have been constructed. The total energy is regarded as consisting of a pair potential part, an embedding interaction part and a modification term. All these parts are analytic functions of the atomic separations only and are fitted to various bulk properties, such as cohesive energy, vacancy formation energy, lattice constant and elastic constants. The present potentials are shown to predict a more realistic pressure–volume relationship so that interactions at separations smaller than that of the first-nearest neighbors can be treated. Interstitial formation energies are calculated for various configurations, using quenched molecular dynamics. Vacancy, surface and phonon spectra have been also studied andsatisfactory agreement with available experimental data has been found.