STRUCTURE-STABILITY RELATIONSHIPS FOR ALL-SILICA STRUCTURES

We will discuss predictions for the stability and structures of all-si lica zeolitic structures. We will show that we have derived a shell-mo del potential, based on ab initio calculations, which gives good predi ctions for the structure and stability of all-silica structures. We wi ll compare three shell-model predictions with two rigid-ion model pred ictions for the structure and stability of silicates. We will show tha t shell-model predictions for the relative stability of zeolites are m uch closer to experiment than rigid-ion model predictions, due to the canceling of covalent and electrostatic terms in the shell models whic h does not occur in the rigid-ion models. Using the potentials with th e highest predictive power on both stabilities and structures of silic ates we will discuss structure-stability relationships that have been proposed in the literature.