Performance of Dispersion-Inclusive Density Functional Theory Methods for Energetic Materials

Area of Science:

• Computational chemistry
• Materials science
• Quantum mechanics

Background:

• Energetic materials (EMs) possess high density and unique nitrogen-containing intermolecular interactions.
• Dispersion-inclusive density functional theory (DFT) methods are crucial for accurately modeling molecular crystals.
• Previous studies have shown success with these methods on other crystal types.

Purpose of the Study:

• To assess the performance of dispersion-inclusive DFT methods for energetic materials.
• To evaluate the impact of vibrational and thermal effects on calculated properties.
• To analyze the sensitivity of intermolecular interactions to DFT approximations.

Main Methods:

• Compiled a dataset of experimental sublimation enthalpies for 31 energetic materials.
• Evaluated Perdew-Burke-Ernzerhof (PBE) with Tkatchenko-Scheffler (TS) dispersion, PBE with many-body dispersion (MBD), and PBE0 with MBD.
• Utilized the quasi-harmonic approximation (QHA) for zero-point energy and thermal effects, including thermal expansion.

Main Results:

• PBE0+MBD yielded the closest lattice energies to experimental sublimation enthalpies (mean absolute error of 9.89 kJ/mol).
• Advanced treatment of vibrational and thermal contributions unexpectedly worsened agreement with experimental data.
• All tested methods showed reasonable agreement (≤3% mean absolute relative error) for pressure-volume curves.
• Intermolecular interactions like nitro-amine and nitro-nitro were more sensitive to dispersion methods, while π-π stacking was sensitive to the exchange-correlation functional.

Conclusions:

• Current dispersion-inclusive DFT methods do not perform as well for energetic materials as for other crystal types.
• The inclusion of thermal expansion is significant for energetic materials.
• Further development of DFT methods is necessary for accurate modeling of energetic materials.