Quantum-chemistry-based force field for simulations of dimethylnitramine

The molecular geometries and conformational energies of nitramide and dimethylnitramine (DMNA), determined from high-level quantum chemistry calculations, have been used in parametrization of a classical potential function suitable for simulations of DMNA. A thorough investigation of basis set size and electron correlation effects on the geometry and conformational energies of nitramide, for which accurate experimental data exist, has allowed us to establish the level of theory required to obtain accurate geometries and energies for nitramine compounds. These investigations revealed the importance of electron correlation for both the geometries and relative conformational energies in nitramines. The quantum-chemistry-based force field for DMNA was validated by comparing gas- and liquid-phase properties obtained from molecular dynamics simulations with available experimental data. The gas-phase radial distribution function obtained from simulation is in good agreement with that obtained from electron diffraction experiments and is consistent with a C-s ground-state geometry for DMNA as predicted by quantum chemistry. The pressure-volume-temperature properties and solubility parameters for the bulk liquid are in very good agreement with available experimental measurements. The correlation time and activation energy associated with molecular reorientation is found to be in good agreement with NMR measurements.