Density functional study of dimers of dimethylnitramine

We have investigated several modes of interaction of two dimethylnitramine molecules. Four functional combinations were tested by comparing the computed (H3C)(2)N-NO2 dissociation energies to the experimental value; the B3PW91 was selected for the dimer calculations. Four different basis sets were used in order to assess the effects of basis set superposition. The computed electrostatic potential on the molecular surface of dimethylnitramine was used to provide guidance as to likely relative orientations for two interacting molecules. Two bound dimers were found, the more stable being produced by two O---H and two O---N interactions, the less stable just by two O---H. Delta E (0 K) and Delta H (298 K) are approximately -3.9 and -3.2 kcal/mol for the first, and -2.6 and -1.8 kcal/mol for the second. The optimized geometries of the dimers show that the monomer components differ significantly from free dimethylnitramine in only one respect, a shortening of the N-N distances by roughly 0.02 Angstrom in the former. The calculated surface electrostatic potentials of the dimers are used to predict likely modes of interaction with a third dimethylnitramine molecule. Their structures are related to that of the crystalline solid. (C) 2000 John Wiley & Sons, Inc.