Predicting the reactivity of energetic materials : an ab initio multi-phonon approach

The ease with which an energetic material (explosives, propellants, and pyrotechnics) can be initiated is a critical parameter to as-sess their safety and application. Impact sensitivity parameters are traditionally derived experimentally, at great cost and risk to safety. In this work we explore a fully ab initio approach based on concepts of vibrational energy transfer to predict impact sensi-tivities for a series of chemically, structurally and energetically diverse molecular materials. The quality of DFT calculations is as-sessed for a subset of the materials by comparison with experimental inelastic neutron scattering spectra (INS). A variety of mod-els are considered, including both qualitative and quantitative analysis of the vibrational spectra. Excellent agreement against ex-perimental impact sensitivity is achieved by consideration of a multi-phonon ladder-type up-pumping mechanism that includes both overtone and combination pathways, and is improved further by the added consideration of temperature. This fully ab initio approach not only permits ranking of energetic materials in terms of their impact sensitivity but also provides a tool to guide the targeted design of advanced energetic compounds with tailored properties.