The normal diffusion regime is defined as the region in which the MSD changes linearly with time. But depending on the nature of the framework-molecule interactions, other (non-linear) diffusion regimes may manifest in the MSD(t) curve. These are often called anomalous diffusion regimes and are described by a power law, MSD(t) = K α t α where K α is the "generalized diffusion coefficient". Several examples of different diffusion regimes are illustrated on Figure and are listed below.