Molecular mechanics and molecular dynamics simulations combined with X-ray powder diffraction were used in structure investigation of montmorillonite intercalated with cetylpyridinium (CP) and cethyltrimethylammonium (CTA) cations. Molecular modeling revealed the interlayer structure and differences in intercalation behavior of CP and CTA cations in montmorillonite. The experimental and calculated values of basal spacing were in good agreement for both intercalates: in the case of CP-montmorillonite d(exp)=20.59 Å, d(calc)=20.60 Å; for CTA-montmorillonite d(exp)=18.00 Å and d(calc)=18.10 Å. CTA-montmorillonite exhibits significantly higher total sublimation energy and higher host-guest interaction energy than the CP-montmorillonite. The main difference between both intercalates is in charge distribution on the host layers and guest species. The charge transfer from the guest species to the host layer is higher in CTA-montmorillonite than in CP-montmorillonite, and consequently the charge polarization between the host and guest layers is much higher in CTA-montmorillonite. This leads to much stronger host-guest electrostatic interaction in the case of CTA-montmorillonite. Copyright 2001 Academic Press.