Structural and Energetic Characterization of Prebiotic Molecules: The Case Study of Formamide and Its Dimer

State-of-the-art quantum-chemical computations have been employed to determine the accurate equilibrium structure of formamide and its symmetric dimer as well as the interaction energy of the latter, thus extending available reference data for the peptide (also denoted as amide) bond and the hydrogen-bond interaction that characterizes peptides and proteins. Equilibrium geometries and electronic energies have been evaluated by means of a composite scheme based on coupled-cluster calculations, including up to triple excitations, which also accounts for extrapolation to the complete basis set limit and core-correlation effects. This approach provides molecular structures with an accuracy of 0.001-0.002 Å and 0.05-0.1° for bond lengths and angles, respectively, and relative energies with an accuracy of about 1-2 kJ/mol.