A theoretical study of molecular structure, optical properties and bond activation of energetic compound FOX-7 under intense electric fields

Analytical Model for the Molecular Ionization Energy in an External Electric Field

A model for the molecular ionization energy in an applied electric field is presented on the basis of a perturbation expansion in the electric field. The leading term arises from the Frenkel approach, which is the same for all molecules normally used in the Poole-Frenkel model for conductivity in an electric field. For a set of test molecules, the quality of the results is comparable to that of previous results using constrained density functional theory. We conclude that the Frenkel term is dominant and sufficient at relatively low fields and that the dipole and polarizability terms, the leading terms dependent on the properties of the individual molecule, make a significant contribution only at high fields and for relatively large molecules. Because the presented model is analytical, quantum chemical calculations are avoided for a variety of electric field strengths and molecular orientations, and the model can therefore be applied directly in coarse-grained models for electronic processes in dielectric condensed phases.

Molecules under external electric field: On the changes in the electronic structure and validity limits of the theoretical predictions

A detailed analysis of the electronic structure of the ground and first excited spin state of three diatomic molecules ( N2, BH and CO) under static applied electric field is performed at CCSD(T), DFT, MRCI and MRCI(Q) levels of theory. Our findings have revealed that by boosting the applied field one induces changes in the occupation numbers of molecular orbitals, giving rise to changes in the equilibrium geometry and in the HOMO-LUMO energy gap. Specifically, singlet to triplet spin transition can be induced by increasing the applied electric field beyond a critical value. Accordingly, affecting the accuracy of the widely used expression of energy expanded in Taylor series with respect to the applied electric field. © 2018 Wiley Periodicals, Inc.

Structural Rearrangement of Energetic Materials under an External Electric Field: A Case Study of Nitromethane

As a significant stimulus, the external electric field (EEF) can change the decomposition mechanism and energy release of energetic materials (EMs). Hence, understanding the response of EMs to an EEF is greatly meaningful for their safe usage. Herein, the structural arrangement, a crucial factor in the impact sensitivity and detonation performance of EMs, under the EEF ranging from 0.0 to 0.5 V/Å was investigated via molecular dynamics simulation. Nitromethane (NM) was taken as a case study due to the simple structure. The simulation results show that there exists a critical EEF strength between 0.2 and 0.3 V/Å, which can induce the transition of NM molecules from relatively disordered distribution to solidlike ordered and compacted arrangement with a large density. In this ordered structure, NM dipoles are aligned in a head-to-tail pattern parallel to the EEF direction because of the favored dipole-dipole interactions and weak C-H···O hydrogen bonds. As the EEF strength is enhanced, the potential energy and cohesive energy density of the NM system gradually decrease and increase, respectively, indicative of high thermodynamics stability of ordered arrangement. The results reported here also shed light on the potential of the EEF to induce the nucleation and crystallization to explore new polymorphs of EMs.

Assessment of various DFT, DFT-D, and MP2 methods for studying FOX-7 detonation properties

B3LYP, PBE, M06-2X, B2PLYP, BN2PLYP-D, ωB97X-D, and MP2 levels of theory, in combination with the 6-311++G(d,p) and cc-pVTZ basis sets were comprehensively assessed for their ability to reproduce experimental FOX-7 structural and detonation data. ωB97X-D/cc-pVTZ, B3LYP/cc-pVTZ, and M06-2X/cc-pVTZ provided highly accurate optimized structure predictions. M06-2X/cc-pVTZ and ωB97X-D/cc-pVTZ reproduced experimentally determined detonation properties (detonation velocity and detonation pressure) with high accuracy. The results of this study demonstrate that more accurate structure calculation levels provide more reliable detonation property predictions. Moreover, the results show that detonation property prediction is largely dependent on the calculation level. This investigation demonstrates that using a wide range of calculation levels enables the reliable prediction and modeling of novel types of HEDMs.