title: Theoretical studies of solid bicyclo-HMX: effects of hydrostatic pressure and temperature.
abstract: On the basis of density functional theory (DFT) and molecular dynamics (MD), the structural, electronic, and mechanical properties of the energetic material bicyclo-HMX have been studied. The crystal structure optimized by the LDA/CA-PZ method compares well with the experimental data. Band structure and density of states calculations indicate that bicyclo-HMX is an insulator with the band gap of ca. 3.4 eV and the N-NO(2) bond is the reaction center. The pressure effect on the bulk structure and properties has been investigated in the range of 0-400 GPa. The crystal structure and electronic character change slightly as the pressure increases from 0 to 10 GPa; when the pressure is over 10 GPa, further increment of the pressure determines significant changes of the structures and large broadening of the electronic bands together with the band gap decreasing sharply. There is a larger compression along the c-axis than along the a- and b-axes. To investigate the influence of temperature on the bulk structure and properties, isothermal-isobaric MD simulations are performed on bicyclo-HMX in the temperature range of 5-400 K. It is found that the increase of temperature does not significantly change the crystal structure. The thermal expansion coefficients calculated for the model indicate anisotropic behavior with slightly larger expansion along the a- and c-axes than along the b-axis.
authors.affiliation: Institute for Computation in Molecular and Material Science, School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, People's Republic of China.
authors.forename: Ling
authors.initials: L
authors.lastname: Qiu
authors.forename: Wei-Hua
authors.initials: WH
authors.lastname: Zhu
authors.forename: Ji-Jun
authors.initials: JJ
authors.lastname: Xiao
authors.forename: He-Ming
authors.initials: HM
authors.lastname: Xiao
mesh_terms: D001643:Bridged Bicyclo Compounds / Q000737:chemistry*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry*; D003198:Computer Simulation; D053834:Explosive Agents / Q000737:chemistry*; D006874:Hydrostatic Pressure; D008956:Models, Chemical; D008968:Molecular Conformation; D013696:Temperature
chemical_list: D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D053834:Explosive Agents