Sodalite framework vibrations

An elegant way to get 0-H vibrational frequencies from short ab initio MD trajectories is based on the monitoring ofroH(t), obtaining the instantaneous vibrational frequencies from the time delay, r, between two consecutive maxima as w = 27r/r. A vibrational density of states can be constmcted from the histogram of the instantaneous frequencies, giving some pieces of information about the expected width of the corresponding IR band. The OH frequency, about 3550 cm , obtained by this procedure from Car-Parrinello PAW trajectories for the sodalite framework is very close to the experimentally expected value. 

Between 3500 and 3600 cm"1 we can observe vibrations due to the OH groups pointing inside the sodalite cavities, i.e. the low frequency band at 3570 cm"1 and the associated band perturbed by the extra framework phase at 3525 cm"1. 

Cation Siting in Linde A. At the time this work was completed, x-ray studies on hydrated NaA (3, 4) and hydrated KA (5) had shown that 8 of the 12 exchangeable cations per unit cell are firmly bound to the zeolite framework and would therefore be expected to have the major influence on the lattice vibrations. These cations are sited in front of the sodalite... 

---