Ceramics-Silikáty 66, (1) 43 - 53 (2022)

Using a classical molecular dynamics (MD) simulation, bulk SiO₂ and Na₂O.3SiO₂ glasses were prepared. Then, glassy systems with surfaces were prepared by two different methods. In the first rather traditional method, the surface of the glass was created by dividing the bulk sample by a plane and inserting a sufficiently thick vacuum layer. The system was then relaxed at elevated temperatures (up to 3000 K). This situation roughly corresponds to the glass-breaking process. In the second method, the surface was present from the beginning and was maintained by an external force field that mimics the wall of the mould. The moulded surface was again relaxed at elevated temperatures (up to 3000 K). This situation roughly corresponds to the glass forming process. The structure of the glass surface was compared with that of basic bulk glass using the radial distribution function of the Si-Si, Si-O, O-O and Na-O pairs, the coordinate numbers and the number of shared edges of the SiO₄ tetrahedra. When the glassy systems with surfaces were compared, the number and density curves of the atoms (Si, O, Na) or groupings (bridging and non-bridging O, Qⁿ units) were used depending on the Z coordinate. It is clear from the comparison that the surface-moulding method generates significantly less surface defects, such as shared edges of SiO₄ tetrahedra (in the case of silica glass), while giving a relatively smoother surface. In the case of the Na₂O.3SiO₂ glass, a notable increase in the sodium cation numbers was found in the surface layer. This study is the initial part of extensive research activities on the topic of functional modifications of glass surfaces.