| Abstract
| - A systematic computational study of gallophosphates was undertaken. First, lattice energyminimization calculations using a formal-charge shell model potential have been carried out on a series ofhypothetical gallium phosphates derived from their metallogallophosphate, aluminophosphate, or aluminosilicate analogues through atomic substitution. The minimized structures show the typical features interms of bond angles and distances as expected in zeolitic gallophosphates. Second, the crystal structuresof several gallophosphates in their calcined forms have been predicted, using for each compound latticeenergy minimization and an initial model derived from its as-synthesized templated form. All the modifiedstructures thus have the same GaPO4 composition. The lattice energies of all the simulated gallophosphatestructures were compared to that of GaPO4-quartz as a reference structure. Interestingly, among all predictedcalcined structures, various zeolitic topologies were found. The study of the energetics of these zeotypicstructures showed a linear dependence of lattice energy upon density. Strikingly, a few simulated structuresshowed unrealistic structural features, such as important framework distortions, often associated with theoccurrence of a hexameric unit in the original as-synthesized structures. Also, those gallophosphates withstructural faults were found in the upper part of the energy/density plot. To address the validity of our forcefield calculations in these special cases, first principles calculations were undertaken on ULM-4, chosenas a typical representative structure. Indeed, the qualitative agreement found between our results andthose obtained with the nonlocal density functional theory demonstrates the robustness of our force field.Further minimizations also showed that the inclusion of polarizability is crucial for yielding results comparablewith those obtained using first principles methods.
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