In the investigations reported here, we have compared the effectiveness of these two procedures with regard to their ability to accurately calculate values of nitrogen-containing energetic compounds. The latter relies on a novel multilevel computational approach known as T1 that approaches the accuracy of the G3MP2 method while simultaneously reducing the computation time by 2-3 orders of magnitude. , was designed to be applicable to a broader range of compounds.
Another procedure, developed by Ohlinger et al. One procedure, developed by Byrd and Rice, uses density functional theory (DFT) coupled with an atom and group contribution method to determine for energetic compounds. During the past several years two relatively rapid computational procedures have been described for use in determining values. Our interest concerns the use of relatively rapid methods for the calculation/prediction of accurate gas-phase heat of formation values. Solid- or liquid-phase values are then calculated by subtracting heat of sublimation ( ) or heat of vaporization ( ) values, respectively, from the gas-phase value. In practice, most theoretical approaches calculate gas-phase heat of formation ( ) values. The condensed-phase heat of formation ( or ) is one of several important parameters used to assess the performance of energetic materials. Manufacturers must be able to determine the amount of energy that can be stored in a molecule while maintaining an acceptable level of stability. Moreover, increasing environmental concerns call for more effective ways of predicting performance of HEDMs. Two important considerations with regard to HEDMs are that they can be dangerous and costly to synthesize. The usefulness of HEDMs in a variety of processes has been understood for at least a century. Collectively, compounds that have densities greater than or equal to 1.9 g/cm 3, detonation velocities greater than or equal to 9.0 km/s, and detonation pressures greater than or equal to 40.0 GPa are known as HEDMs. There is substantial interest in the discovery and development of new energetic compounds which include high explosives and propellants and there is special interest in the discovery and development of high energy density materials (HEDMs). Although semiempirical methods continue to improve, they were found to be less accurate than the other approaches for the test set used in this investigation. We also compared two relatively new semiempirical approaches (PM7 and RM1) with regard to their ability to accurately calculate. The T1 procedure and Benson’s group additivity method yielded results in which 51% (23 of 45) and 64% (23 of 36) of the values, respectively, were within ☒.0 kcal/mol of these values. This was compared to a procedure using density functional theory (DFT) coupled with an atom and group contribution method in which 51% (23 of 45) of the values were within ☒.0 kcal/mol of these values. Density functional theory coupled with the use of isodesmic or other balanced equations yielded calculated results in which 82% (37 of 45) of the values were within ☒.0 kcal/mol of the most recently recommended experimental/reference values available.
We evaluated the ability of six different methods to accurately calculate gas-phase heat of formation ( ) values for a test set of 45 nitrogen-containing energetic compounds. Heat of formation is one of several important parameters used to assess the performance of energetic compounds.
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