This is the accepted manuscript. The final version is available at via http://dx.doi.org/10.1039/C5CC06455D ; We present experimental and computational evidence that gate-opening modes for zeolitic imidazole frameworks can be observed at terahertz frequencies. Our work highlights the critical importance to correctly optimise the crystal structure prior to computational lattice dynamics analysis. The results support the hypothesis that the low energy vibrational modes do indeed play a significant role in host-guest interactions for ZIFs, such as gas loading. ; C.O.T. thanks Becas Chile and the Cambridge Trust for funding; D.F.-J. thanks the Royal Society (U.K.) for funding through a University Research Fellowship. T.M.K. would like to acknowledge the Royal Society as well as the Royal Society of Chemistry for support.