Computational Studies of Aluminum Phosphate Polymorphs

• Published in: Chemistry of materials 1996-03, Vol.8 (3), p.664-670
• Main Authors: Henson, Neil J, Cheetham, Anthony K, Gale, Julian D
• Format: Article
• Language: English
• Subjects: Chemistry; Condensed matter: structure, mechanical and thermal properties; Crystalline state (including molecular motions in solids); Exact sciences and technology; General and physical chemistry; Ion-exchange; Other ion exchangers: preparations and properties; Physics; Structure of solids and liquids; crystallography; Surface and interface chemistry; Surface physical chemistry; Theory of crystal structure, crystal symmetry; calculations and modeling
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm9503238

Lattice energy minimization calculations have been carried out on a series of aluminum phosphate polymorphs using a formal charge shell model potential. The experimental structures are reproduced to a reasonable accuracy, especially in cases where high-quality crystallographic data are available on calcined structures. Good agreement is also found with previous calculations on these systems. In cases where the experimental methods give conflicting results regarding the space-group symmetry, calculated structures having lower symmetry than those observed in the crystallographic studies are suggested. An approximately linear dependence of lattice energy on density is observed; the computed lattice energies are found to span a range of 11.7 kJ mol-1 higher than berlinite, which compares to an experimentally determined range of 9.7 kJ mol-1. Proton binding calculations have been performed on the structure of H-SAPO-37 to determine the most favorable proton sites. Both periodic and isolated defect cluster calculations correctly reproduce the sites which have the highest fractional occupancies in a crystallographic study.