Abstract

Classical energy minimisation techniques have been employed to model the effect of hydration on the adsorption behaviour of extra-framework cations Na⁺, Cs⁺, Ca²⁺, Ba²⁺, Cd²⁺ and Sr²⁺ in zeolite A. The experimental structure of zeolite CaNa-A (Si/Al = 1) is reproduced accurately, while the energetically preferred position for water molecules is calculated to be inside the α-cage, in agreement with experiment. The preferential locations for the sodium and calcium ions in the hydrated zeolite A are governed by the water molecules and are calculated in the siliceous structure to be the β-cages (S6R position) for Na⁺ and β-cages (S6R′ positions) for Ca²⁺. These locations are in agreement with experimental findings of zeolite A structures, but have not previously been calculated for the calcium position.