A generation of framework structures for the tectosilicates using a molecular-based potential energy function and simulated annealing strategies

More than 1400 framework model structures have been derived using simulated annealing strategies and the geometry and a potential energy function calc ulated for the disilicic acid molecule. The derivation was undertaken start ing with either 3 or 6 formula units of SiO2 randomly distributed in a unit cell of variable geometry and P1 space group symmetry. More than 40 model low energy structures are described, including quartz and a mixed stacking sequences of tridymite and cristobalite. As observed in earlier calculation s with 4 formula units per unit cell, the tridymite topology was not genera ted. In addition to model structures that match or relate to the framework structures of the zeolites NaJ, bikitaite, sodalite and cancrinite, model s tructures with Si networks were derived that match those enumerated by Smit h [J.V. Smith, Am. Min. 62 (1977) 703] and O'Keeffe and Brese [M. O'Keeffe, N.E. Brese, Acta Cryst. A48 (1992) 663]. A number of the model structures are apparently new and have yet to be described and cataloged. The successf ul derivation of the known structure types of silica and the framework mode ls of known tectosilicates using molecular models, indicate that the forces that govern the structure of silica behave as if short ranged. (C) 1999 El sevier Science B.V. All rights reserved.