Structural, vibrational, and quasiparticle band structure of 1,1-diamino-2,2-dinitroethelene from ab initio calculations

Abstract

The effect of pressure on the structural and vibrational properties of the layered molecular crystal 1,1-diamino-2,2-dinitroethelene (FOX-7) are explored by first principles calculations. We observe significant changes in the calculated structural properties with different corrections for treating van der Waals interactions to Density Functional Theory (DFT), as compared with standard DFT functionals. In particular, the calculated ground state lattice parameters, volume and bulk modulus obtained with Grimme's scheme are found to agree well with experiments. The calculated vibrational frequencies demonstrates the dependence of the intra and inter-molecular interactions in FOX-7 under pressure. In addition, we also found a significant increment in the N-H...O hydrogen bond strength under compression. This is explained by the change in bond lengths between nitrogen, hydrogen and oxygen atoms, as well as calculated IR spectra under pressure. Finally, the computed band gap is about 2.3 eV with GGA, and is enhanced to 5.1 eV with the GW approximation, which reveals the importance of performing quasiparticle calculations in high energy density materials.

Dispersion Corrected Structural Properties and Quasiparticle Band Gaps of Several Organic Energetic Solids

“…There have been promising attempts made to fix this shortcoming, and considerable benchmarking studies are available with advanced methods for noble gas solids, layered, sparse and molecular crystals. [22][23][24][25][26][27][28][29][30][31][32] In the case of energetic materials, Sorescu et al 33 35 From our previous studies on nitromethane and FOX-7 solids, 36,37 we also found good agreement using Grimme and TS methods. However, it is observed that although the mentioned dispersion corrected methods overcomes most of the difficulty in reproducing ground state volumes, the relative errors still show a mean absolute deviation of about 3 %.…”

“…43,44 But the well known disagreement of the computed band gap using standard DFT functionals leads to an inaccurate estimation of the properties related to the band gap either in molecular or solid systems. However from our previous studies on some energetic materials (solid nitromethane, FOX-7, cynauric triazide) 36,37,45 and another theoretical study on TATB by Fedorov et al, 46 it is known that the GW approximation [47][48][49][50][51][52] can overcome this problem.…”

Structural, vibrational and bonding properties of hydro-nitrogen solids under high pressure: An ab-initio study

“…Owing to the presence of hydrogen bonding, it can be expected that the N-H strengthening frequency decreases (red-shift) with increasing pressure and this red-shift leads to strengthening of hydrogen bonding. 28 In addition, our previous 37,38 studies on hydrogen bonded systems, and those of Pravica et al, 39 suggest that the red-/blue-shift in the mid-IR frequencies stabilizes/destabilizes the system under high pressure. Therefore, in the present study, we have also calculated the IR spectra under pressure up to 30 GPa to get spectroscopic picture of the hydrogen bonding for the TMAA and HZA compounds under hydrostatic compression.…”

High-pressure stability of 1,1-diamino-2,2-dinitroethene (FOX-7): H/D isotope effect

“…Although its low sensitivity to impact and shock waves is of considerable interest, the microscopic factors governing this behavior are not well understood. To gain insight into this behavior several experimental [6][7][8][9][10] and theoretical [11][12][13][14][15] studies have been conducted to characterize the molecular response of FOX-7 at high pressures. In accord with its low sensitivity to initiation, it was recently shown that FOX-7 single crystals are chemically stable over a broad range of pressure [10].…”