Theoretical study on highly nitrated sensitive pyrazole isomers in the presence of external electric field

Context: This article mainly studies three isomers of C₅H₃N₇O₁₀, namely 5-methyl-3,4-dinitro-1- (trinitromethyl) -1H pyrazole (1), 4-methyl-3,5-dinitro-1- (trinitromethyl) -1H pyrazole (2), and 3,5-bis (dinitromethyl) -4-nitro-1H-pyrazole (3). These three substances are excellent candidates for energetic materials, but their properties under external electric fields (EEF) have not been studied. Therefore, this article studied the properties of three isomers under EEF using density functional theory (DFT), and conducted statistical analysis on the obtained data, including the molecular structure, frontier molecular orbitals, surface electrostatic potential, and nitrate charge of the three isomers. The results showed that applying EEF to the trigger bonds of 1 and 2 increased bond length, leading to a decrease in material stability. The change in bond length induced by 3 was relatively stable, and the results obtained from calculating the nitro charge were consistent with the bond length results. When an EEF is applied to three substances, the polarization degree of the molecules of the three substances increases. It is worth mentioning that the polarization degree of the molecules under the influence of a negative EEF is greater than that of a positive EEF.

Methods: Using density functional theory, the B3LYP/6-311 + G (d, p) method was employed for structural optimization. After optimizing convergence, ensure that there are no imaginary frequencies to obtain a stable structure. Wave function analysis was performed using Multiwfn 3.8 and VMD 1.9.3. The EEF strength ranged from - 0.02 a.u. to 0.02 a.u., with a growth gradient of 0.005 a.u.