Evaluation of electric field within pores of aluminophosphate sieves


  • The contribution is dedicated to Dr. Enrico Clementi who pioneered high-level quantum mechanical calculations on large systems.


A new way to evaluate the electric field (EF) based on the propagation of multipole moments distributed over atomic sites is illustrated for arbitrary aluminophosphate (ALPO) sieves of ratio Al/P = 1. The atomic multipole moments (AMMs) are evaluated for all crystallographic independent atomic types of 10 ALPO structures within the scheme developed by Saunders and colleagues, considering the electron density computed with the CRYSTAL 98 code at the periodic density functional theory (PDFT) level and different basis sets. In two steps, the method uses the calculated AMMs to calibrate several approximate dependences and permits construction of molecular charge distributions for any sieve. First, atomic charges are evaluated via fitted analytical expressions versus the atomic geometries of the framework. Second, high AMMs up to hexadecapole are approximated for all atomic positions, using a cumulative coordinate scheme. Differences between calculated and approximated EF values within the porous space available for adsorbed molecules are discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005