The Cumulative Coordinate Method for Describing the Electrostatic Potential and Field in Silica Zeolite Polymorphs

Hartree-Fock calculations with periodic boundary conditions were performed for the X-ray structure models of all-silica zeolites to determine the dependences of atomic multipole moments up to the fourth order inclusive with respect to the so-called cumulative coordinate. These dependences were used to describe the electrostatic potential and electric field in cross sections of several zeolites. The description was shown to be satisfactory provided the atomic charges were known. The deviations of atomic multipole moments in strongly distorted structures from those determined using the approximation suggested are discussed. The applicability scope of the cumulative coordinate method to all-silica zeolites is considered.