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 t he electronic structure zeolite NaCaA. A model system of composition C a8Na8Si24Al24O96 is produced, with <F(4)over bar 3c> symmetry and stri ct alternate ordering of silicon and aluminum. The positions of the Na and Ca cations were optimized using the RHF/STO-3G level of theory. P roperties of the crystal, such as the partial charges and bond populat ions, the electrostatic potential, and the electric field within the z eolite 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 crystall ographic studies. The calculated RHF/6-21G field of the zeolite is ne gligible in the center of both the alpha- and beta-cage, but rises qui ckly close to the cation centers.