A semiempirical QM/MM implementation and its application to the absorptionof organic molecules in zeolites

An intermolecular hybrid semiempirical MO/molecular mechanics technique is described. The model allows polarisation of the quantum mechanical molecule (s), but not of the molecular mechanics part and is shown to be relatively insensitive to the size of the molecular mechanics environment. It has been validated by comparison of calculated and experimental absorption energies of small organic molecules in various zeolites. This validation gives us c onfidence that the method is also appropriate for experimentally less well characterised problems, such as solvation or ligand/enzyme complexation.