Abstract:In computational thermochemistry, “isodesmic‐type” reactions play a significant role for obtaining accurate thermochemical quantities using low‐cost methods that can be applied to large systems. This review touches on some of the examples. For instance, a series of relative bond dissociation energies (BDEs) have been devised to calculate absolute BDEs with near‐chemical‐accuracy (~5 kJ mol−1) using density functional theory (DFT) methods. To facilitate the applicability of isodesmic‐type reactions, the connect… Show more
“…Any intrinsic error associated with calculating any particular chemical bond is thereby cancelled out, meaning that relatively low-level computational methods can be employed to give fairly accurate results ( Hehre et al, 1970 ). This method has been employed in computational chemistry for over 50 years, with recent developments automating the generation of parts of the isodesmic reaction equation ( Chan et al, 2020 ). However, as a general technique it has found little application beyond CHNO-containing molecules.…”
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.
“…Any intrinsic error associated with calculating any particular chemical bond is thereby cancelled out, meaning that relatively low-level computational methods can be employed to give fairly accurate results ( Hehre et al, 1970 ). This method has been employed in computational chemistry for over 50 years, with recent developments automating the generation of parts of the isodesmic reaction equation ( Chan et al, 2020 ). However, as a general technique it has found little application beyond CHNO-containing molecules.…”
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.
“…23. Using the WGh composite procedure developed by Chan 38 and unifying the W1X 39 and the G4(MP2)-6X 40 protocols, the predicted enthalpy of formation of coronene, C 24 H 12 , via an isodesmic-type reaction 41,42 was found to be 13.8 kJ mol −1 lower compared to that in ref. 23.…”
We introduce a protocol aimed at reducing the dependence of predicted gas-phase heats of formation of polycyclic aromatic hydrocarbons (PAH) via the reaction-based Feller-Peterson-Dixon approach. Automatic generation of a dataset...
“…Bond dissociation enthalpies (BDEs) are a central property in chemistry that have been studied for decades experimentally and computationally 1 – 4 . BDEs can be used to estimate the selectivity and reactivity of various molecules with free radicals (like · OH, · OOH, · OR, · OOR, · NO, · NO 2 , etc.)…”
We present an extensive and diverse dataset of bond separation energies associated with the homolytic cleavage of covalently bonded molecules (A-B) into their corresponding radical fragments (A. and B.). Our dataset contains two different classifications of model structures referred to as “Existing” (molecules with associated experimental data) and “Hypothetical” (molecules with no associated experimental data). In total, the dataset consists of 4502 datapoints (1969 datapoints from the Existing and 2533 datapoints from the Hypothetical classes). The dataset covers 49 unique X-Y type single bonds (except H-H, H-F, and H-Cl), where X and Y are H, B, C, N, O, F, Si, P, S, and Cl atoms. All the reference data was calculated at the (RO)CBS-QB3 level of theory. The reference bond separation energies are non-relativistic ground-state energy differences and contain no zero-point energy corrections. This new dataset of bond separation energies (BSE49) is presented as a high-quality reference dataset for assessing and developing computational chemistry methods.
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