Institut pluridisciplinaire de recherche sur l'environnement et les matériaux, UMR 5254 du C.N.R.S. et de l'Université de Pau et des pays de l'Adour, avenue Pierre Angot, Pau Cedex 64053, France.
J Chem Phys. 2010 Mar 7;132(9):094501. doi: 10.1063/1.3314286.
Molecular 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 [B. W. H. van Beest et al., Phys. Rev. Lett. 64, 1955 (1990)], but with reduced partial atomic 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 molecular diffusion constants of water. Two types of adsorption, specific and weak unspecific, are predicted on the channel walls and at the channel intersection. We discuss molecular diffusion of water in silicalite, deducing a barrier to crossing between the straight and the zigzag channels. Analysis of the thermal motion shows that at room temperature, framework oxygen atoms incurring into the zeolite channels significantly influence the dynamics of adsorbed water.
采用一种新的力场对纯硅沸石 silicalite（MFI 骨架代码）进行分子动力学模拟，该力场既保持了骨架的灵活性，又能真实地考虑与吸附水的静电相互作用。该力场类似于著名的“BKS”模型[B. W. H. van Beest 等人，Phys. Rev. Lett. 64, 1955 (1990)]，但部分原子电荷减小，共价键势阱重新优化。目前的力场再现了 silicalite 的单斜到正交的转变。该力场正确地表示了纯硅沸石 silicalite 的疏水性，包括吸附能和水分子的扩散常数。在通道壁和通道交叉处预测了两种吸附类型，即特异性吸附和弱非特异性吸附。我们讨论了水在 silicalite 中的扩散，推断出直通道和之字形通道之间的跨越势垒。对热运动的分析表明，在室温下，进入沸石通道的骨架氧原子会显著影响吸附水的动力学。
