Simulations of Fluid Nitromethane Under Extreme Conditions Page: 4 of 6
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constant-volume and temperature conditions. The
studied state is in the neighborhood of the
Chapman-Jouget state, which is achieved behind a
steady detonation front when the material has fully
reacted. This state could be achieved through a
sudden heating of nitromethane in a diamond anvil
cell under constant volume conditions. Our results
emphatically show that the first chemical event is a
proton extraction to form CH3NO2H, the aci ion
H2CNO2 , and the aci acid H2CNO2 H. These
results are uniquely associated with the condensed-
phase rather than the energetically favored C-N
decomposition expected in the gas-phase.
molecules. The unit cell was fully optimized at the
reduced (compressed) volume, V = 205.36 A3.
RESULTS AND DISCUSSION
The initial configuration at density 1.974 g/cm3
was determined by compressing the simulation cell
and performing full relaxation of all atomic
coordinates. From this initial structure, molecular
dynamics were performed using the Nose-Hoover
thermostat at 3000K.
The electronic structure calculations of the
molecular forces were performed using density
functional theory (DFT). s For the exchange-
correlation potential, we used the spin-polarized
generalized gradient corrected approximation of
Perdew -Wang (PW91). 9 Electron-ion interactions
were described by Vanderbilt-type ultrasoft
pseudopotentials, 10 and orbitals were expanded in
a plane wave basis set with kinetic energy cutoff of
340 eV. We used two k-point spacing in the
Brillouin zone, each with a total number of 2921
plane waves. Minimization of the total density
functional from DFT utilized the charge density
mixing scheme. " Calculations on a single unit cell
were performed using the CASTEP program ,2
while those on larger cells employed the VASP
Molecular dynamics simulations were carried
out under constant volume and temperature using a
Nose thermostat. For each MD run, random initial
velocities were chosen, and a first-order Verlet
extrapolation of the wave functions was used.
Periodic boundary conditions, whereby a particle
exiting the cell on one side is reintroduced on the
opposing side with the same velocity were
imposed. A dynamical time step of 0.25 fs was
employed for all runs, the longest of which was 4.5
ps. Simulations were performed at a constant
temperature of 3000 K using either one unit cell of
nitromethane crystal (4 molecules, 28 atoms), a
supercell with 8 molecules, and a supercell with 16
-b \p 4...
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Fried, L E; Reed, E J & Manaa, M R. Simulations of Fluid Nitromethane Under Extreme Conditions, article, July 15, 2003; California. (https://digital.library.unt.edu/ark:/67531/metadc1418361/m1/4/: accessed May 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.