Generation and study of a relatively large amorphous silica surface in the liquid phase

ABSTRACT

Through the classical and ab-initio molecular dynamics computer simulations, the aim of this study was to generate and analyse a surface-type structure in the liquid phase at a temperature of 3400 K. First, a crystalline structure was used (β-cristobalite) with 216 SiO₂ molecules (648 atoms) and it was melted. Next, the resulting structure was properly cut, with a total of 546 particles remaining, and this system was put into a geometric arrangement denominated ‘sandwich’, where it was equilibrated. The prior processes were implemented through the classical molecular dynamics computer simulations using the effective classical potential of Feuston [B. P. Feuston and S. H. Garofalini, J. Chem. Phys. 89, 5818 (1988)]. Finally, the electronic charge distribution and topological and bonding defects were analysed in the first five superior layers of this system. This latter was carried out through the ab-initio molecular dynamics computer simulations, where the pseudopotentials of N. Trouiller and J. L. Martins [N. Trouiller, J. L. Martins, Phys. Rev. B 43, 1993 (1991)] were used. The results show different aspects between them, the interaction between the bonding and topological defects, and the existence of two-membered rings, nonbridging oxygens (NBOs) and three-coordinated silicon at the outermost surface.

KEYWORDS:

• β-cristobalite
• silica nanoparticles
• SIESTA
• molecular dynamics simulation