Effects of silica cluster size and charge state on integral characteristics

Abstract

The model sizes of solid particles as well as used quantum chemical methods can affect results of calculations with density functional theory (DFT) methods. The aim of this study was to analyze the effects of the silica cluster sizes, a number of bound water molecules, protonation and deprotonation of silanols, addition of Eigen cation alone or solvated, attachment of anions F- and Cl- alone or solvated, and whole solvation effects (with SMD) with the DFT calculations using a functional ωB97X-D with the cc-pVDZ basis set. The calculations of the distribution functions of atom charges (CDF), chemical shifts of the proton resonance (SDF), and integral density of electron states (IDES) show that small clusters with 8 or 22 (SiO4/2) units could give rather inappropriate results in contrast to larger clusters with 44 or 88 units. This is due to the fact that the small silica clusters do not have appropriate capability for delocalization of excess charges that leads to certain distortion of the electron states of the whole system. The IDES are more sensitive with respect to the cluster charging and less sensitive to the solvation effects than the CDF and SDF. As a whole, the use of several types of the distribution functions, such as integral characteristics with the CDF, SDF, and IDES, allows one to obtain a more detailed picture on the interfacial phenomena at silica surface for neutral and charged systems.