Application of SCC-tight-binding to reactive systems at extreme conditions

M. Riad Manaa, manaa1@llnl.gov, Evan Reed, Kurt Glaesemann, and Laurence
Fried. Chemistry and Materials Science, Lawrence Livermore National Laboratory,
7000 East Avenue, P.O. Box 808, L-282, Livermore, CA 94551

A typical shock wave produces a pressure 500,000 times that of the Earth's
atmosphere, traveling as fast as several kilometers per second, and raising the
internal temperature of the system up to 5,500 Kelvin. These conditions initiate
fast and complex chemical reactions in organic molecular solids. Our effort is
geared toward unraveling detailed decomposition pathways and effective kinetic
rate laws of stable products at the high-pressure and temperature
conditions. The self-consistent charge, density functional based tight binding
method has been implemented in a new, efficient, multi-scale shock wave
simulation technique to study the chemistry of nitromethane at shock speeds
ranging from 5.5 up to 8 km/s for an extended time of several hundreds
picoseconds. These simulations represent the farthest glimpse to date behind the
shock front in a chemically reactive molecular dynamics simulation of reactive
materials. Kinetic rate laws for decomposition products, and early chemical
reaction mechanisms will be discussed for several of these simulations.