Force field methods practical considerations

This synopsis summarises three applications of the hybrid method, two of which actually involve chemical reactions. The combination of a semiempirical kernel and a force-field environment has been very successful in these application and has yielded information that could - at present - be obtained by other means (experimental or computational) only with considerable difficulty or not at all. One has to realise, though, that in practice there is a window of usefulness of the method If the energy differences are large enough the energetics will be mainly determined by vacuum values, i.e. environment effects will be negligible. If, on the other hand, the energy differences are small compared to the intrinsic inaccuracies of semiempirical method and force field the results cannot be trusted. 

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