The repulsive Lennard-Jones nonbonded parameters for the conformational study of neutral peptide molecules are developed. This repulsive nonbonded potential energy is consistent with the electrostatic interaction energy calculated with modified-PEOE charges, the attractive Lennard-Jones nonbonded potential energy, and the hydrogen-bond potential energy, which were developed previously. Both equilibrium conditions of molecules in molecular crystals and lattice energies of molecular crystals were used as constraints during the determination of the repulsive nonbonded potential parameters. The reliability of the optimized parameters was tested by crystal packing studies. The crystals used as constraints are paraffins, conjugated ring compounds, sulfur containing hydrocarbons, carboxylic acids, and amides. The calculated properties of the molecular crystals, lattice energies and lattice cell parameters, agree well with experimental values. A complete set of intermolecular potential functions for neutral peptides was prepared in a self-consistent manner.