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.

Using molecular dynamics simulations and a modified analytic embedded-atom method (MAEAM), the relaxations and vibrations of Ni(977) surface are studied in the temperature range of 100–1500K, The calculated results for the temperature dependence of phonon frequencies, line-width and the mean square amplitude show that the anharmonic effects are small for temperatures up to 900K. The calculated interlayer separation for the first and second surface decreases, and the distance along the x direction increases between the topmost and second surface, with increasing temperature. In addition, the calculated layer structure factor indicates that the Ni(977) surface is well ordered and does not premelt up to a temperature of 1700K.

Simple modified analytic embedded atom method(MAEAM)many-body potentials are constructed for bcc molybdenum and hcp rhenium metal in the present paper. Using the MAEAM and analytic alloy potentials, the segregation profiles for(100)surface in Mo–Re bcc-type random alloys were studied with Monte Carlo simulation technology. The simulation results show that the topmost surface is almost completely enriched with molybdenum, the subsurface is depleted of molybdenum, and the molybdenum concentration oscillates toward the bulk value. The simulation results are in good agreement with available low-energy electron diraction and low-energy ion scattering experiment data, and the calculations from tight-binding Ising model.

Molecular dynamics calculations have been performed to study the melting evolution, atomic diffusion and vibrational behavior of bcc metal vanadium nanoparticles with the number of atoms ranging from 537 to 28475 (diameters around 2-9 nm). The interactions between atoms are described using an analytic embedded-atom method. The obtained results reveal that the melting temperatures of nanoparticles are inversely proportional to the reciprocal of the nanoparticle size, and are in good agreement with the predictions of the thermodynamic liquid-drop model. The melting process can be described as occurring in two stages, firstly the stepwise premelting of the surface layer with a thickness of 2-3 times the perfect lattice constant, and then the abrupt overall melting of the whole cluster. The heats of fusion of nanoparticles are also inversely proportional to the reciprocal of the nanoparticle size. The diffusion is mainly localized to the surface layer at low temperatures and increases with the reduction of nanoparticle size, with the temperature being held constant. The radial mean square vibration amplitude (RMSVA) is developed to study the anharmonic effect on surface shells.

Isothermal grain growth behaviors, including the effect of temperature and mean grain size, of nanocrystalline Ag are investigated using the molecular dynamics simulations with an analytical embedded atom potential. The atomistic simulations provide a level of atomic details on microscopic mechanism and process of grain growth that still remains inaccessible to experiments. The small grain size and high temperature accelerate the grain growth, it is the same as the conventional polycrystalline materials. The grain growth processes of nanocrystalline Ag are well characterized by a power-law growth curve, followed by a linear relaxation stage. Beside grain boundary migration and grain rotation mechanisms, the dislocations(or stacking faults)serve as the intermediate role in the grain growth process.