Unique stoichiometric representation for computational thermochemistry

Evaluation of the enthalpy of formation of species via quantum chemical methods, as well as the evaluation of their performance, is mainly based on single reaction schemes, i.e., reaction schemes that involve a minimal number of reference species where minimal means that, if a reference species is omitted, there is no way to write a balanced reaction scheme involving the remaining species. When the number of reference species exceeds the minimal number, the main problem of computational thermochemistry is inevitably becoming an optimization problem. In this communication we present an exact and unique solution of the optimization problem in computational thermochemistry along with a stoichiometric interpretation of the solution. Namely, we prove that the optimization problem may be identically solved by enumerating a finite and unique set of reactions referred to as group additivity (GA) response reactions (RERs).