Abstract
The reliable determination of gas-phase and solid-state heats of formation are important considerations in energetic materials research. Herein, the ability of PM7 to calculate the gas-phase heats of formation for CNHO-only and inorganic compounds has been critically evaluated, and for the former, comparisons drawn with isodesmic equations and atom equivalence methods. Routes to obtain solid-state heats of formation for a range of single-component molecular solids, salts, and co-crystals were also evaluated. Finally, local vibrational mode analysis has been used to calculate bond length/force constant curves for seven different chemical bonds occurring in CHNO-containing molecules, which allow for rapid identification of the weakest bond, opening up great potential to rationalise decomposition pathways. Both metrics are important tools in rationalising the design of new energetic materials through computational screening processes.
Highlights
Energetic materials are characterised by their ability to rapidly convert chemical potential energy into kinetic energy
Computational screening presents an attractive route in the new materials pipeline, as it offers a cost-effective way to assess candidates prior to synthesis
Local vibrational mode analysis has been carried out on 30 molecules containing chemical bonds found in energetic molecules, to evaluate bond length/strength relationships and to ascertain the likely weakest bonds in energetic molecules
Summary
Energetic materials (explosives, propellants, pyrotechnics and gas generators, EMs) are characterised by their ability to rapidly convert chemical potential energy into kinetic energy. Atom equivalence energy values for the four atoms were determined through comparison of experimental heats of formation for molecules in a training set and their computationally derived molecular energies (Byrd and Rice, 2006) This method works well, reporting root mean square deviation of 12.6 kJ mol−1 and is arguably more efficient than the isodesmic equation route, as it requires just the optimised energy of the molecule of interest expressed at a prescribed quantum mechanical model chemistry. Local vibrational mode analysis has been carried out on 30 molecules containing chemical bonds found in energetic molecules, to evaluate bond length/strength relationships and to ascertain the likely weakest bonds in energetic molecules Both parameters have been highlighted for their potential to be included in a computational screening program for new energetic materials
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