Quantum Chemistry Methods for the Prediction of Molecular Thermochemistry

Quantum Chemistry Methods for the Prediction of Molecular Thermochemistry 

As discussed above, accurate thermochemical data are an essential component of the development of any gas-phase chemical mechanism. For the purposes of this work, accurate generally means knowing heats of formation to 2-3 kcalmol It is evident that much of the speculation in the literature 

From a computational point of view, the heat of formation, which is derived from the electronic energy of the molecule molecule is the most difficult thermochemical quantity to predict accurately. Entropies and heat capacities are derived from vibration and rotational constants, all of which can be predicted with considerable accuracy using relatively low levels of theory. Thus, the development of ab initio methods appropriate for a new class of compounds focuses primarily on identifying a level of theory and the basis set(s) needed to achieve sufficient accuracy in the electronic energy [67,68]. 

Once the electronic energy has been calculated, the molecular heat of formation AW is calculated as follows  

A theoretical approach that we find predicts main-group thermochemistry quite successfully is the BAG method [67,72-74]. To date, BAG methods have been applied to and thermochemistry reported for compounds of boron [75,76], carbon [73,77], nitrogen [73], aluminum [76,78], sihcon [72,79-86], and galUiun [76]. The BAG methodology recognizes that 

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