SiO2(111) surface optimization by DFT calculations

A. DIAZ COMPAÑY; G. ROMAN; A. JUAN; S. SIMONETTI

Conferencia; 7th International Conference on Advanced Nanomaterials; 2016

The development of modern theoretical surface science provides an opportunity to investigate structures on the atomic scale with useful applications in industrial technologies. Due to their high surface areas and pore volumes, mesoporous silicas have attracted great attention in novel applications.Calculations reported in this work were performed in the framework of the Density Functional Theory (DFT) using the Vienna Ab-initio Simulation Package. In this code plane wave basis sets are used to solve the Kohn?Sham equations. The electron projector augmented wave (PAW) method was used and the generalized gradient approximation (GGA) with the Perdew?Burke?Ernzerhof (PBE) functional was utilized. The fixed convergence of the plane-wave expansion was found with cut-off energy of 750 eV. A set of 3×3×1 Monkhorst-Pack k-points was used to sample the Brillouin Zone. The ground state was found by a Methfessel-Paxton smearing of 0.2eV. The SiO2(111) surface model is obtained from bulk β-cristobalite, saturated with OH groups and optimized by DFT calculations. The result is a silica surface model whose density of silanols is close to the experimentally measured value for fully hydroxylated surface. The SiO2(111) surface was represented with a periodically repeated slab containing five layers of atoms (the optimum number of layers was previously tested) separated in the normal direction by a vacuum region. The width of this gap was optimized to avoid the interaction between slabs.