High-Pressure Behavior And Spectracopic Properties Of Engetic Materials: Atomic Simulations

This dissertation is devoted to the study of behavior and spectroscopic properties of energetic materials under high pressure and high temperature, with classical molecular dynamic and first-principle methods. Understanding structure in molecular details and bonding behaviors under extreme condition has become essential to advance this particular area of science and technology.1. We performed classical molecular dynamic simulations of liquid nitromethane under high compression and high temperature. The classical potential of CHARMM type was used in the MD simulations. More than 60 individual MD simulations (of at least 50 ps each) were carried out with 108 molecules in the simulation supercell. Although our simulations roughly reproduce the trend of thermodynamic functions, for example, the shock velocity is more or less a linear function of the particle velocity, the calculated results of Hugoniot pressure are too high at given density as compared to experimental data and other MD simulations with different potential functions. The interatomic repulsive interaction is overestimated in the Lenard-Jones potential functional. Overall, almost all potential now don't perform well at high pressure. To overcome it, one has to develop a new potential function whose repulsive part is soft enough to describe the compressibility of nitromethane liquid under high pressure.2. The structural, vibrational, and electronic properties of solid nitromethane under hydrostatic pressure up to 20 GPa have been studied using density functional theory. The changes of cell volume, the lattice constants, and the molecular geometry of solid nitromethane under hydrostatic loading are examined, and the bulk modulus B₀ and its pressure derivative B₀ are fitted from the volume-pressure relation. Our theoretical results are compared with available experiments. The change of electron band gap of nitromethane under high pressure is also discussed. Based on the optimized crystal structures, the vibrational frequencies for the internal and lattice modes of the nitromethane...