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.

In the atomic scale, the melting behaviors of nanocrystalline Ag with mean grain size ranging from 3.03 to 12.12 nm have been investigated with molecular dynamics simulations, and a method to determine the melting temperatures of the infinite polycrystalline nanostructured materials is presented. It is found that the melting in nanostructured polycrystals starts from their grain boundaries, and the relative numbers of the three typical bonded pairs, (1551), (1431), and (1541), existing in the liquid phase, increase rapidly with the evolvement of melting. The melting temperatures of nanocrystalline Ag decrease with decreasing mean grain size, and it can be estimated from the size-dependent melting temperature of the corresponding nanoparticles.

In the present paper, the size and temperature effects on lattice distortion of Ag and Pt nanoparticles have been investigated in terms of atomic mean bond length using the molecular dynamics simulations and the modified analytic embedded atom method. It is found that the lattice contraction ratio decreases linearly with the reciprocal of the particle size. The average value of lattice contraction over the whole system is larger than that of the experimental data, and the average value of lattice contraction in the inner core has a better agreement with the experiment results. This phenomenon is mainly resulted by inhomogeneous lattice distortion. The surface distortion and the size effect on the inner core distortion are remarkable. As the grain size increases to a certain degree, the inhomogeneous surface lattice distortion is mainly localized to the outer shell with a thickness of 2-3 lattice parameters.

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.

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.