A systematic method of deriving atom-atom intermolecular potentials from the monomer wave functions has been developed for formamide, acetamide and tl trans-N-methylacetanlide (NMA) and tested for its ability to reproduce the crystal structures. The total intermolecular potentials comprised an accurate distributed multipole analysis representation of the multipolar electrostatic interaction energy, an atom-atom Cg dispersion model, and a short-range repulsion model derived from the overlap of the monomer charge densities. The short-range model has been assessed and validated by comparison with ab initio intermolecular perturbation theory (IMPT) calculations of the exchange-repulsion, penetration, and charge-transfer energies of test sets of around 20 dimer conformations. A range of models has been developed. The simplest version of the overlap model need not require any IMPT calculations (though in this example they are used to calibrate and validate the potential) and can be used to estimate atom-atom repulsive parameters. Removal of various simplifying assumptions in the overlap model gives better reproductions of the IMPT data and the crystal structures, and provides a route to specific potentials for organic molecules. The resulting model potentials, as assessed by crystal structure reproduction, are comparable with the best empirical potentials for amides and superior to some commonly used potential energy functions. An advantage of the method is that transferability of parameters can be tested, rather than assumed. There is an encouraging degree of transferability as the potential generated for NMA reproduces the crystal structures of formamide and bothpolymorphs of acetamide very well.