Improved Hill-Sauer Force Field for Accurate Description of Pores in 8-Ring Zeolites

We have introduced a simple modification of the well-known Hill-Sauer force field for silica. The modified force field improves the accuracy with which pore sizes and framework flexibility in small pore zeolites are described. The modification focused on the Si-O-Si and O-Si-O angles in these materials, which are instrumental in controlling vibrations of the framework such as twisting of the near-rigid SiO4 units. The accuracy of the modified Hill-Sauer force field was compared with data from extensive density functional theory calculations of zeolite structures and dynamics. The transferability of the force field was tested on 13 experimentally known silica 8-ring zeolites. Additional tests examining the thermal expansion behavior of selected zeolites were also performed.