Weak intermolecular bonding in N,N′-dimethylethyleneurea dimers and N,N′-dimethylethyleneurea-water systems: The role of the dispersion effects in intermolecular interaction

Using first principle quantum chemical methods based on Hartree-Fock, density functional theory and second order Møller-Plesset perturbational theory, equilibrium configurations of N,N′-dimethylethyleneurea (DMEU) dimer and DMEU-water systems were studied using the D95**+ full double-zeta, cc-pVXZ and aug-cc-pVXZ (X = D, T, Q) basis sets. Three different structures for DMEU dimer and two for DMEU-water systems were found. Method of the symmetry-adapted perturbational theory was applied for intermolecular interaction energy decomposition in order to elucidate the role of the physically relevant energy components. For all studied equilibrium configurations, dispersion effects are significant, while the contributions of the other energy components are relatively smaller. Two out of the three studied configurations of the DMEU dimers are strong enough to be not destroyed by binding with further water molecules. Such configurations are suggested to play role in dilute aqueous solutions of DMEU, in which DMEU aggregation was recently observed.