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 comput ed (H3C)(2)N-NO2 dissociation energies to the experimental value; the B3PW9 1 was selected for the dimer calculations. Four different basis sets were u sed 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 interac ting 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/mo l for the first, and -2.6 and -1.8 kcal/mol for the second. The optimized g eometries of the dimers show that the monomer components differ significant ly 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 e lectrostatic potentials of the dimers are used to predict likely modes of i nteraction with a third dimethylnitramine molecule. Their structures are re lated to that of the crystalline solid. (C) 2000 John Wiley & Sons, Inc.