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By employing a first-principles method, we conducted a thorough study on a novel cocrystal explosive 1 : 1 NTO : TZTN and gained insight into the interaction-structure-property interrelationship. Mulliken bond orders, Hirshfeld surfaces, intermolecular binding energies, packing coefficients, and oxygen balance were calculated to analyze the intermolecular interactions and structures of the cocrystal explosive. The cocrystallization of NTO and TZTN molecules enhances the intermolecular binding force, which drives the synthesis of the cocrystal. However, the cocrystallization decreases the molecular packing density along the closest packed directions, which reduces the density by 10.5% and deteriorates the oxygen balance. All of these lead to a reduction in the detonation performance compared to NTO explosives. We have also proposed a new method to evaluate the impact sensitivity according to the lattice dynamics calculation. The cocrystal explosive has a lower impact sensitivity than TZTN but higher than NTO, which agrees well with experiments.

We perform ab initio simulations of beryllium (Be) and magnesium oxide (MgO) at megabar pressures and compare their structural and thermodynamic properties. We make a detailed comparison of our two recently derived phase diagrams of Be [Wu et al., Phys. Rev. B 104, 014103 (2021)] and MgO [Soubiran and Militzer, Phys. Rev. Lett. 125, 175701 (2020)] using the thermodynamic integration technique, as they exhibit striking similarities regarding their shape. We explore whether the Lindemann criterion can explain the melting temperatures of these materials through the calculation of the Debye temperature at high pressure. From our free energy calculations, we obtained a melting curve for Be that is well represented by the fit Tm(P) = 1564K*[1 + P/(15.8037 GPa)]^0.414 , and a melting line of MgO, which can be well reproduced by the fit Tm(P) = 3010K*(1 + P/a)^(1/c) with a = 10.5797 GPa and c = 2.8683 for the B1 phase and a = 26.1163 GPa and c = 2.2426 for the B2 phase. Both materials exhibit negative Clapeyron slopes on the boundaries between the two solid phases that are strongly affected by anharmonic effects, which also influences the location of the solid-solid-liquid triple point. We find that the quasi-harmonic approximation underestimates the stability range of the low-pressure phases, namely hcp for Be and B1 for MgO. We also compute the phonon dispersion relations at low and high pressure for each of the phases of these materials, and also explore how the phonon density of states is modified by temperature. Finally, we derive secondary shock Hugoniot curves in addition to the principal Hugoniot curve for both materials, and study their offsets in pressure between solid and liquid branches.