A DENSITY-FUNCTIONAL STUDY OF SODALITE - A NEW VIEW ON AN OLD SYSTEM

We have conducted a first principles calculation of sodalite (Na8Cl2Al 6Si6O24) to explore the structural properties of aluminosilicate frame works. By isolating Al-poor and rich frameworks, with and without extr a-framework ions, we show that framework interaction with extra-framew ork ions is not the origin of the so-called framework collapse - as pr eviously believed. Instead, this collapse is a direct consequence of f ramework stresses resulting from aluminum substitution, We find that e xtra-framework ions play only a weak role in determining the structura l configuration of sodalite - a new result that should apply to open z eolite structures in general. (C) 1998 Elsevier Science B.V.