Periodic Hartree−Fock Characterization of the Structure and Electronic Properties of Zeolite NaCaA

In this paper we present an ab initio periodic Hartree−Fock study of the electronic structure zeolite NaCaA. A model system of composition Ca 8 Na 8 Si 24 Al 24 O 96 is produced, with F 4̄3 c symmetry and strict alternate ordering of silicon and aluminum. The positions of the Na and Ca cations were optimized using the RHF/STO-3G level of theory. Properties of the crystal, such as the partial charges and bond populations, the electrostatic potential, and the electric field within the zeolite cage, were calculated at the more accurate RHF/6-21G* level of theory. Results indicate that the cations are situated slightly above the 6-ring units, in agreement with recent experimental X-ray crystallographic studies. The calculated RHF/6-21G* field of the zeolite is negligible in the center of both the α- and β-cage, but rises quickly close to the cation centers.