A new theoretical insight into the nature of intermolecular interactions in the molecular crystal of urea

The nature of interactions in the molecular crystal of urea is analyzed in terms of the interaction energy decomposition. The influence of the electron correlation effects was estimated on the basis of the calculated second order Moller-Plesset corrections and their analysis. In the crystal, the urea molecules form infinite ribbons which reveal strong cooperative effects. The hydrogen-bonded interactions of the orthogonal ribbons do stabilize the crystal, whereas interactions between parallel tapes are repulsive. The stability of the crystal structure is determined by a subtle balance between these two types of interactions. Although, the electron correlation effects are stabilizing, their contribution is rather small in comparison with the total interaction energy. (C) 2002 American Institute of Physics.