Ab initio predictions of zeolite structures and 29Si NMR chemical shifts.

A recent shell-model potential parameterized on ab initio data is used for predicting the all-silica structures of zeolites MFI, MEI, MTW, TON, FAU and of alpha-quartz. Cluster models are defined around each site and the 29Si NMR shielding constants are calculated by ab initio techniques (GIAO-HF). Good agreement with observed 29Si NMR chemical shifts is found. Comparison is made with shifts calculated for observed structures. The structures predicted by the ab initio shell-model potential prove as accurate as the observed ones when judged on the quality of the calculated 29Si NMR spectra.