In order to obtain smooth potential energy surfaces, domains must be frozen. The domain information can be stored using the SAVE option and recovered using the START option. Alternatively, the SAVE and START can be used, see section 28.8.3. In the latter case, also the CCSD amplitudes are saved/restarted. Freezing domains is particularly important in calculations of intermolecular interactions, see section 28.9.8. Domains that are appropriate for larger ranges of geometries, such as reaction pathways, can be generated using the MERGEDOM directive, section 28.8.6. The domains are automatically frozen in geometry optimizations and frequency calculations, see section 28.9.7.