A molecular dynamics simulation of thermodynamic properties of 1, 3, 5-triamino-2, 4, 6-trinitrobenzene under high pressure and high temperature

Abstract

Equation of states and thermodynamic properties of insensitive high explosive 1, 3, 5-triamino-2, 4, 6-trinitrobenzene (TATB) are investigated by using molecular dynamics simulation, where an all-atom force field for TATB developed by Richard H. Gee and isothermal-isobaric molecular dynamics (NPT-MD) methods are used. Results obtained include thermal expansion coefficient, elastic constants, tensile modulus, and debye frequency under high temperature and high pressure. The volume coefficient of thermal expansion for crystalline TATB is calculated in a temperature range of 200 to 500 K and at atmospheric pressure. The result, 35.910-5 K-1, is in general agreements with the experimental results. Results of elastic constants show that the crystalline TATB is an orthotropic material. The calculated elastic constants decrease with increasing temperature in the range from 0 to 450 K, while increase as the pressure increases from 0 to 50 GPa. And the bulk modulus at 300 K is 11.32 GPa, which is in good agreement with the available experimental results. Results obtained above have been compared with available experimental data, and also discussed in relation to the previous calculations. The above results are better than existing ones gained by others. In addition, the elastic anisotropy becomes lower with increasing temperature or pressure. As the temperature goes up to 400 K, the lattice becomes unstable. The sound speed and Debye frequency are calculated by using the data of elastic constants at different pressures. This provides a theoretical basis to calculate the anisotropic thermal conductivity for crystalline TATB.