COMPUTATIONAL STUDIES OF SI AL ORDERING IN ALUMINOSILICATE TETRAHEDRAL FRAMEWORK STRUCTURES/

An extensive computational research programme on Si/Al ordering in tet rahedral framework structures is surveyed. Earlier results on the enth alpy of ordering are briefly reviewed, and their reliability discussed in the light of rib initio calculations. The main reason is discussed why the ordering temperature often lies well below that expected from Bragg Williams theory, with new quantitative results. The actual path way of Si/Al ordering appears complex from some inconclusive nb initio calculations, but the presence of hydrogen clearly lowers the barrier substantially.