Host and adsorbate dynamics in silicates with flexible frameworks: Empirical force field simulation of water in silicalite

International audienceMol. dynamics simulations are performed on the pure silica zeolite silicalite (MFI framework code), maintaining via a new force field both framework flexibility and realistic account of electrostatic interactions with adsorbed water. The force field is similar to the well-known "BKS" model, but with reduced partial at. charges and reoptimized covalent bond potential wells. The present force field reproduces the monoclinic to orthorhombic transition of silicalite. The force field correctly represents the hydrophobicity of pure silica silicalite, both the adsorption energy, and the mol. diffusion consts. of water. Two types of adsorption, specific and weak unspecific, are predicted on the channel walls and at the channel intersection. We discuss mol. diffusion of water in silicalite, deducing a barrier to crossing between the straight and the zigzag channels. Anal. of the thermal motion shows that at room temp., framework oxygen atoms incurring into the zeolite channels significantly influence the dynamics of adsorbed wate