Temperature-dependent shear viscosity coefficient of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX): A molecular dynamics simulation study

Equilibrium molecular dynamics methods were used in conjunction with linear response theory and a recently published potential-energy surface [J. Phys . Chem. B 103, 3570 (1999)] to compute the liquid shear viscosity and self- diffusion coefficient of the high explosive HMX (octahydro-1,3,5,7-tetranit ro-1,3,5,7-tetrazocine) over the temperature domain 550-800 K. Predicted va lues of the shear viscosity range from 0.0055 Pa *s at the highest temperat ure studied up to 0.45 Pa *s for temperatures near the melting point. The r esults, which represent the first publication of the shear viscosity of HMX , are found to be described by an Arrhenius rate law over the entire temper ature domain studied. The apparent activation energy for the shear viscosit y is found to scale with the heat of vaporization in a fashion consistent w ith those for a wide variety of simple nonmetallic liquids. The self-diffus ion coefficient, which requires significantly shorter trajectories than the shear viscosity for accurate calculation, also exhibits an Arrhenius tempe rature dependence over the simulated temperature domain. This has potential ly important implications for predictions of the shear viscosity at tempera tures near the melting point. (C) 2000 American Institute of Physics. [S002 1- 9606(00)50613-8].