Dimethylformamide clusters: non-covalent bondings, structures and temperature-dependence

Thermodynamics properties as well as infrared spectra of liquids can be determined using the quantum cluster equilibrium (QCE) theory. The QCE theory requires the knowledge of the structures of the clusters formed by the solvent molecules. In prelude to this determination, in this work, we studied the non-covalent bondings, the structures and the temperature-dependence of the clusters of dimethylformamide (DMF) from dimer to tetramer. To perform this study, we used classical molecular dynamics to sample initial geometries of DMF clusters. Then, optimisation of the geometries is carried out at the MP2/aug-cc-pVDZ level of theory. Besides, we carried out a quantum theory of atoms in molecule analysis. The results show that the structures of the DMF dimer exhibit a stacking configuration, and mainly stabilised by CH··· O hydrogen bondings. For the DMF trimer and DMF tetramer, the structures exhibit an amorphous behaviour. Moreover, it has been found that the CH··· O hydrogen bondings are the main non-covalent bondings in DMF clusters. CH··· C, CH··· N, N··· O, N··· C, C··· O and H··· H bonding interactions are also located in the studied DMF clusters. In addition, the temperature-dependence study shows that only isomers with relative energy within ∼ 1.0 kcal/mol have meaningful contribution to the population of DMF clusters.