Prediction of ADN/ANF cocrystal and its theoretical properties

Abstract

Context

Ammonium dinitramide (ADN) is highly hygroscopic, which poses significant challenges in its practical applications. Consequently, mitigating this hygroscopic nature has been a primary focus in the research and development of ADN. This study investigated the properties of the ADN/3-amino-4-nitrofurazan (ANF) cocrystal using density functional theory, molecular dynamics, and Monte Carlo methods. The research involved analyzing binding energies, radial distribution functions, and molecular interaction energies; predicting crystallographic properties of the cocrystal; and ADN theoretically assessing its hygroscopic and detonation properties. The results indicated that the cocrystal achieved relative stability at a 1:1 molar ratio of ADN to ANF, driven by favorable conditions for cocrystal formation. The primary forces facilitating this cocrystal formation were electrostatic and van der Waals interactions. The predicted space group for the cocrystal was P21-C, with a calculated crystal density of 1.8836 g·cm⁻³. Additionally, the cocrystal demonstrated a calculated saturated moisture absorption rate of 9.07%, which contrasted significantly with the 18.12% absorption rate observed for pure ADN. Theoretical calculations indicated that the detonation performance of the cocrystal surpassed that of the pure components ADN and ANF, suggesting that the ADN/ANF cocrystal was a new type of high-energy material with low hygroscopicity.

Methods

For the whole molecular dynamics simulation, the simulation was done in Materials Studio 2020 software, under NPT ensemble, with a set temperature of 298 K, a pressure of 0.0001 GPa, a temperature control of Andersen, and a pressure control of Berendsen. The total simulation time was 1 ns. The first 0.5 ns was used for the thermodynamic equilibrium, and the second 0.5 ns was used for statistical calculations and analysis. It was used for statistical calculations and analysis. Samples were recorded every 10 fs during the calculation. All systems were simulated similarly. Surface electrostatic potentials were calculated using Gaussian and Multiwfn programs with B3LYP, 6-31G +  + basis sets, and levels. Hygroscopicity calculations utilized the Sorption module to simulate pure ADN and ADN/ANF cocrystals. Water was chosen as the adsorbate, with a pressure of 2.813 kPa, temperature set at 308.15 K, and adsorbate coverage ranging from 0.12 to 0.8.