Structural, electronic, vibrational, and thermodynamic properties of a novel energetic ionic 2,6-diamino-1‑hydroxy-9H-purine-1,7-diium nitrate

Abstract

Nitrogen-rich energetic salts have garnered growing interest owing to their flexible molecular frameworks and adjustable energetic behavior, highlighting the importance of investigating energetic ionic compounds. However, theoretical studies on the newly synthesized nitrate-based energetic salt, 2,6-diamino-1-hydroxy-9H-purine-1,7-diium nitrate, remain scarce. In this work, first-principles calculations are employed to comprehensively explore its structural, electronic, vibrational, and thermodynamic characteristics. The optimized lattice parameters exhibit excellent agreement with available experimental X-ray diffraction data, confirming the reliability of the computational approach. The electronic characteristics are analyzed through the band structure and the partial density of states (PDOS) of atomic valence electrons. The phonon density of states and dispersion curves are plotted, and the contributions of different atomic groups are discussed in detail. Furthermore, characteristic vibrational modes are assigned, and the calculated infrared spectra show good consistency with experimental frequencies. Based on vibrational properties, thermodynamic functions including entropy (S), enthalpy (H), constant-volume heat capacity (C_V), and Debye temperature (Θ) are calculated as functions of temperature. These results not only bridge the current gap in experimental thermodynamic data for this compound but also provide theoretical insights and a valuable reference for future experimental validation and performance evaluation.

This work is based on first-principles calculations within the framework of density functional theory (DFT), using the CASTEP software. The exchange–correlation functional is treated using the Perdew-Burke-Ernzerhof (PBE) method within the generalized gradient approximation (GGA), along with Grimme’s dispersion correction.