Electrostatic potential (EP) and electric field (EF) values are calculated in periodic models of proton-substituted brewsterite (HBRE) and chabazite (HCHA) zeolite forms using the periodic DFT (PDFT) hybrid B3LYP level with 13 different basis sets. Relative root mean square differences between the EP, or EF, values estimated between the different basis sets are evaluated in several spatial domains available for adsorbate molecules in both zeolites. In these areas, the EF increase in HCHA is evaluated relative to all-siliceous CHA. The EP is interpreted in terms of ionicity of the framework. © 2007 Wiley Periodicals, Inc.