New Efficient methods to Characterize Effects of Framework Flexibility on CH4 Diffusion in 8MR Zeolites

Molecular dynamics and transition state theory predicts diffusion of molecules in nanoporous materials. To save computational time, the framework of the material is assumed rigid which may or may not be accurate. In our study, we systematically characterize the effect of framework flexibility on diffusion in model zeolites that exhibit different patterns of window flexibility. We show that for molecules with kinetic diameters comparable (or larger) to the size of the window the rigid framework approximation can produce order(s) of magnitude difference in diffusivities as compared to the simulations performed with a fully flexible framework.. To account for framework flexibility effects efficiently and reliably, we introduce two new methods in which the flexible structure is approximated as a set of discrete rigid snapshots obtained from molecular dynamics simulations of an empty framework, using classical method. Both methods are orders of magnitude more efficient than the simulations with the fully flexible structure.