A molecular dynamics simulation has been carried out to investigate the dynamics heterogeneity SiO2 liquid at 2600 K and ambient pressure. We indicate that the diffusion in the liquid is realized by the rate of effective reaction, SiOx®SiOx’ and OSiy®OSiy’. Moreover, the reactions are non-uniform happened, but they are spatially clustered. In addition, we found the clustering from different sets of atoms specified by the mobility of atom or frequency of reactions. We found that the clustering become more pronounced at ambient pressure. This evidences the dynamics heterogeneity in the SiO2 liquid.

We use the molecular dynamics simulation to study iron nanoparticles (NP) which consist of 5000 atoms at temperatures of 450 and 850 K. The crystallization and structure evolution was analyzed through pair radial distribution function, transition to different x-types, with x is the bcc, fcc and hcp, ico, 14, 12, and dynamical structure parameters. Simulation results that at 450 K, NP contains a large number of ico-type atoms which play a role in preventing of crystallization. The crystallization happened when NP was annealed at 850 K for 40 ns. Transitions to bcc-type do not happen arbitrarily at any location in NP, but instead they are focused in a non-equilibrium region. We showed that the crystallization pathway includes intermediate states between amorphous and crystalline phases. Firstly, a large cluster of cryst-atom is formed in a middle layer of NP. Next, this cluster grows up and the parameter for this cluster increases rapidly. Finally, the cluster of cryst-atom is located in a well-equilibrium region covered a major part of NP. The structure of crystalline NP is strongly heterogeneous and consists of separate local structure regions.

No abstract

The structural phase transformation and crystallization of amorphous silica at 500 K under high pressure are investigated by molecular dynamics simulation. Under compression, there is a structural transformation from tetrahedral- to octahedral-network via SiO5 units. Structural transformation occurs strongly in the 5–15 GPa pressure range and there exist three structural phases corresponding to SiO4, SiO5, and SiO6. Beyond 15 GPa, octahedral-network is dominant. At pressure higher than 20 GPa, octahedral network tends to transform to crystalline phase (stishovite). Mechanism of structural transformation is clarified via coordination-number, bond-angle distributions, bond length distribution, and 3D visualization. The size-distribution of phase regions is also determined in this work.

This study reported a simulation of structural transition and correlation between structural and dynamical heterogeneity (DH) for liquid Al2O3. Structural characteristics of liquid Al2O3 were clarified through the pair radial distribution functions, the distribution of [Formula: see text] and [Formula: see text] ([Formula: see text], 4, 5, 6; [Formula: see text], 2, 3) basic structural units, angle and bond length distribution and 3D visualization. Simulation results revealed that network structure of liquid Al2O3 is built mainly by AlO3, AlO4, AlO5 and AlO6 units that are linked to each other through common oxygen atoms. We found the existence of separate AlO4-, AlO5- and AlO6-phases where the mobility of atoms can be determined. The atoms in AlO4-phase are more mobile than the ones in AlO5- and AlO6-phases. The existence of separate phases is evidence of DH in liquid Al2O3. Moreover, the self-diffusion of Al and O atoms was also discussed via characteristics of separate AlO4-, AlO5- and AlO6-phases.