Periodic B3-LYP calculations on H-Edingtonites, both alone and interactingwith acetylene

The EDI framework has been adopted, for the first time, to define a series of zeolites derived from the all-silica Edingtonite, featuring a tetragonal lattice with five SiO2 groups per unit cell, by substitution of a single S i atom per unit cell by an Al atom and the addition of a charge compensatin g acidic proton. Four different H-EDI structures have been considered, the geometries of which have been obtained by minimizing the mechanical energy defined in terms of a model ion potential force field. The relative stabili ty and the anharmonic OH-stretching frequency have been computed for the re sulting optimized geometries by an nb initio periodic method using the B3-L YP hamiltonian and polarized basis set of double zeta quality. The electros tatic potential and the electric field within the zeolite cavity have also been computed ab initio. The interaction of acetylene with a given H-EDI st ructure has then been studied at the ab initio B3-LYP level, by optimizing selected degrees of freedom. The binding energy and the OH frequency shift due to interaction with acetylene have been computed and compared with thos e from molecular cluster models containing the Bronsted site. From energeti c and vibrational data of the interaction with acetylene, the periodic stru cture appears more acidic than the adopted model clusters. The H-EDI zeolit e appears to be an attractive model system for its structural simplicity wh ich allows one to study the interaction of small probe molecules using mode rate computational resources.