Molecular dynamics simulations of surface-initiated melting of nitromethane.

The melting of nitromethane initiated at solid-vacuum interfaces has been investigated using molecular dynamics nvt simulations with a realistic force field [D. C. Sorescu et al., J. Phys. Chem. B 104, 8406 (2000)]. The calculated melting point (251+/-5 K) is in good agreement with experiment (244.73 K) and values obtained previously (approximately 255.5 and 266.5+/-8 K) using other simulation methods [P. M. Agrawal et al., J. Chem. Phys. 119, 9617 (2003)]. Analyses of the molecular orientations and diffusion during the simulations as functions of the distance from the exposed surfaces show that the melting is a direct crystal-to-liquid transition, in which the molecules first gain rotational freedom, then mobility. There is a slight dependence of the melting temperature on the exposed crystallographic face.