FFSiOH: a New Force Field for Silica Polymorphs and Their Hydroxylated Surfaces Based on Periodic B3LYP Calculations

A partial charge shell-ion model potential for silica polymorphs and their hydroxylated surfaces (FFSiOH) was parametrized in a self-consistent way using periodic B3LYP results for bulk α-cristobalite and the (100) and (001) hydroxylated surfaces. The reliability of the new potentials was checked by comparing structures, vibrational frequencies and relative phase stabilities of dense bulk silica polymorphs, namely α-quartz, α-cristobalite, α-tridymite, and Stishovite with both experimental and B3LYP data. The FFSiOH was also checked for computing structural and vibrational features of representative all-silica microporous materials, namely edingtonite, chabazite, and faujasite. As a last step, FFSiOH was adopted to predict OH stretching vibrational frequencies and relative thermodynamic stability of the most common fully hydroxylated surfaces of the dense silica polymorphs, the (100) and (001) faces of all-silica edingtonite, the features of the local Si-defect in chabazite and sodalite known as (SiOH)4 hydrogarnet and the geometries of H-bonded silanol groups of an amorphous silica surface. In all cases excellent agreement resulted between FFSiOH and B3LYP periodic data and experimental data, when available. The new FFSiOH force field opens up the molecular simulation of materials in which the surface hydroxyl groups play a key role, as is the case for amorphous silica surfaces, all-silica zeolite external surfaces, and the internal walls of mesoporous materials.