Molecular dynamics simulation of amorphous SiO2 spherical nanoparticles has been carried out in a model with different sizes, 2, 4, and 6 nm, under non-periodic boundary conditions. We use the pair interatomic potentials which have weak Coulomb interaction and Morse type short-range interaction. Models have been obtained by cooling from the melt via molecular dynamics (MD) simulation. Structural properties of amorphous nanoparticles obtained at 350 K have been studied via partial radial distribution functions (PRDFs), mean interatomic distances, coordination numbers, and bond-angle distributions, which are compared with those observed in the bulk. Calculations of the radial density profile in nanoparticles show the tendency of oxygen to concentrate at the surface as observed previously in other amorphous clusters or thin films. Size effects on structure of nanosized models are significant. The calculations show that if the size is larger than 4 nm, amorphous SiO2 nanoparticles have a distorted tetrahedral network structure with the mean coordination number ZSi-O approximately 4.0 and ZO-Si approximately 2.0 like those observed in the bulk. Surface structure, surface energy, and glass transition temperature of SiO2 nanoparticles have been obtained and presented.

Structural properties of liquid and amorphous TiO 2 have been studied in a model containing 3000 particles under periodic boundary conditions with the pairwise interatomic potentials proposed by Matsui and Akaogi. Models have been obtained by cooling from the melt via molecular dynamics (MD) simulation. Structural properties of an amorphous model obtained at 350 K have been analyzed in details through the partial radial distribution functions (PRDFs), coordination number distributions, bond-angle distributions and interatomic distances. Calculations show that calculated data agree well with the experimental ones. The evolution of structure upon cooling from the melt was observed and discussed. Calculations show that amorphous TiO 2 has a distorted octahedral network structure with the mean coordination number

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Melting of monatomic glass with free surfaces has been studied by molecular dynamics simulations in models with Lennard-Jones-Gauss interatomic potential. Models have been heated up from a glassy state toward a normal liquid state. Atomic mechanism of melting has been analyzed via monitoring spatio-temporal arrangements of liquid-like atoms occurred during heating process. Liquid-like atoms are detected via the Lindemann criterion of melting. It is clear that the transition from glass into supercooled liquid of our "ordinary" glass with free surfaces exhibits a non-heterogeneous behavior, i.e., although liquid-like atoms initiate/grow mainly in the surface shell, significant amount of liquid-like atoms also initiates/grows simultaneously in the interior during heating process. We found three characteristic temperatures of melting of glass with a free surface. Temperature dependence of structure and various thermodynamic quantities of the system upon heating is also presented and discussed.

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