Approximation of the Mulliken-type charges for the oxygen atoms of all-siliceous zeolites

Distributed multipole analysis on the basis of periodic Hartree-Fock (PHF) calculations, using the CRYSTAL code, is applied to 12 all-siliceous zeolite models, plus one H-form type. A simple approximation of the dependence of the Mulliken-type charge of the framework oxygens, calculated with two Gaussian basis sets, is found with respect to the average Si-O distance and Si-O-Si angle. These results allow the estimation of the oxygen charges within zeolites with larger elementary unit cells which are still hardly tractable with the presently available computing facilities. The validity of such an estimation for the oxygens of silicalite is shown by comparison with results of direct PHF calculations.