| Abstract
| - While the topology of the molecular sieve AlPO4-5 (structure type AFI) is well established, details of thestructure determined experimentally, such as the precise space group, have varied significantly since its firstsynthesis 25 years ago. Classical molecular dynamics simulations with several force fields, periodic ab initioenergy minimization, and ab initio magnetic-shielding calculations are therefore applied here to models ofcalcined AlPO4-5 and other aluminophosphates and compared to experimental data to help to resolveexperimental discrepancies. Empirical models with partial atomic charges are overall in better agreementwith a range of diffraction and NMR data for AlPO4-5 and other aluminophosphate sieves, than is a modelwith formal cation charges and polarizable oxygens. An order−disorder transition is found in the model,which may explain disagreements in the literature. It is predicted to occur close to room temperature from atriclinic to an on average hexagonal space group. Periodic ab initio and density functional theory calculationsconfirm that the space group of the most stable structure is not P6cc.
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