Samsung Advanced Institute of Technology

 Accurate melting point prediction is essential for investigating the molecular mechanisms

of crystal growth and melting using molecular dynamics (MD) simulations.

Here, we report melting point predictions from direct MD simulations of nitromethane

and acetic acid. This study has three objectives: to evaluate popular force fields

(CGenFF, OPLS, GAFF), to assess various MD approaches (simulations of solid/liquid,

vapor/solid/liquid/vapor, vapor/solid/vapor, and solid alone), and to compare the crystal

growth and melting of both compounds, focusing specifically on the timescale and

anisotropy. Our results indicate that none of the popular force fields accurately predict

melting points, highlighting the need for improvement. All MD simulation approaches

yielded consistent melting points, except for the solid-alone simulation, while continuous

heating of the vapor/solid/vapor system proved effective. The timescales of crystal

growth and melting differ significantly between the molecules: 20 ns for nitromethane

and 200 ns for acetic acid. Anisotropy in crystal growth and melting is non-negligible

and much more pronounced for acetic acid compared to nitromethane. This study

provides guidelines for MD-based melting point predictions of molecular crystals.