Direct Simulation of Detonation Products Equation of State by a Composite Monte Carlo Method

Computer simulations are presented for a Composite Monte Carlo method, which allows direct simulation of 'real' explosives such as HMX and TATB. Chemical equilibrium, solid carbon, fluid-fluid phase separation, and the like, are all included in a single simulation method. Now, the entire detonation products equation of state can be simulated instead of isolated portions for limited benchmarks. The solid carbon phases (bulk and/or cluster) are incorporated using analytic models, while the fluid components are explicitly included in the Monte Carlo simulation. Chemical reactions are treated by a correlated interchange of atoms between species. Solid carbon enters as virtual particles with an associated Gibbs free energy. Simulations for HMX, PBX 9501 and PBX 9502 products cover a range of pressures up to 80 GPa and temperatures up to 5000 K. Starting with potentials chosen for good agreement with single fluid EOS data, the strong dependence of the EOS on cross potentials is demonstrated. This includes chemical equilibrium composition and shifts in the fluid-fluid phase separation lines. Detonation velocity versus density, overdriven Hugoniot, and isentropes are determined from interpolation of a tabulation over a dense set of states in the independent variables P and T.