On the accuracy of force fields for predicting the physical properties of dimethylnitramine.

The accuracy of three force fields for predicting the physical properties of dimethylnitramine (DMNA) has been investigated by using molecular dynamics simulations. The Sorescu, Rice, and Thompson (SRT) (J. Phys. Chem. B 1997, 101, 798) rigid-molecule, flexible generalized AMBER (J. Comput. Chem. 2004, 25, 1157), and Smith et al. flexible force fields (J. Phys. Chem. B 1999, 103, 705) were tested. The density, lattice parameters, isotherm, and melting point of DMNA are calculated using classical molecular dynamics. Except for the melting point, the predictions of the three force fields are in reasonable agreement with experimental values. The calculated thermodynamic melting points (Tmp) for the SRT, AMBER, and Smith et al. force fields are 380, 360, and 260 K, respectively. The experimental value is 331 K. Modifications of the torsional barriers in the AMBER force field resulted in Tmp = 346 K, in good agreement with the experimental value of 331 K. The calculated lattice parameters and bulk modulus are also improved with the modifications of the AMBER potential. The results indicate that, although not sufficiently accurate without modifications, the general force fields such as AMBER provide the basis for developing force fields that correctly predict the physical properties of nitramines.