Simulated annealing method for determining atomic distributions from NMR data: Silicon and aluminum in faujasite

Simulated annealing is applied to the determination of distributions of silicon and aluminum atoms on the faujasite lattice from Si-29 NMR data. The method is described and compared to others. The local silicon environments, Si(nAl), n = 0-4, are reproduced to high accuracy by the technique. More detailed features of local structure are then available, such as numbers of Al on different ring systems in the zeolite. Dempsey's rule is found to be strictly followed in the four rings of the zeolite X sample studied, while this is not the case for zeolite Y-in agreement with previous work. The results are consistent with a possible small violation of Lowenstein's rule in the zeolite X sample.