Force-field simulated stability of nanoscopic SiO2 and MgO clusters

To determine the dependence of lattice energy on particle size, static force-field and Mott–Littleton simulations of nanoscopic and sub-nanoscopic SiO2 and MgO clusters have been performed on the basis of energy minimization, using electrostatic and covalent interatomic potentials. Clusters were defined as spherical fragments of crystals inside an infinite cell. The initial crystallographic data of the clusters satisfied those of β-cristobalite and periclase, diameters reaching from 0.2 nm to 4.2 nm, what, in total, results in a cluster size of up to 2000 atoms. During energy minimization, the structure of the cluster undergoes a relaxation process, leading to structural changes especially at the surface of the cluster until a stable non-crystalline state is achieved. Calculating the difference between the lattice energy of the structural state before and after relaxation allows the determination of the amorphization radius of the material. In the case of SiO2 and MgO clusters, an amorphization radius at room temperature of 1.4 nm and 1.7 nm, respectively, was found. The results are analyzed in terms of cluster formation in SiO2 and MgO liquids. It is demonstrated that the presented technique might be a new way to access the critical nucleation radius.