AN AB-INITIO PERIODIC HARTREE-FOCK STUDY OF GROUP IA CATIONS IN ANA-TYPE ZEOLITES

This study investigates the electronic structure of Group IA cations intercalated into zeolites with the analcime (ANA) framework using ab initio periodic Hartree-Fock theory. The purpose of the study is to gain a better understanding of the role played by electron-donating species in zeolites in general, with specific applications to materials that have been suggested as storage matrices for radioactive materials. The effect of the intercalated species (Na, K, Rb, and Cs) on the electronic structure of the zeolite is presented on the basis of an analysis of the total and projected density of states, Mulliken charges, and charge density differences. The results of those analyses indicate that, relative to a charge neutral atomic state, the Group IA species donate an electron to the zeolite lattice and interact most strongly with the s and p atomic states of oxygen as the species are moved through the lattice. In addition, estimates of the self-diffusion constants of Na, K, Rb, and Cs based upon a one-dimensional diffusion model parameterized from the ab initio total energy data will be presented. We find that the estimated self-diffusion rate decreased markedly with increasing cation size, and that the diffusion rate of Cs was essentially zero in bulk pollucite. The cationic charge is unchanged as the species moves through the lattice. This indicates that model potentials based upon an ionic interpretation of the Group IA species may be reasonable.