#Absolute entropy table free

Prediction of thermochemistry is crucial for designing chemicals with new functionality since fundamental properties such as Gibbs free energy, enthalpy, heat capacity, and standard entropy are needed to understand stability and reaction energies of compounds.

Finally, in order to facilitate the analysis of thermodynamics properties by others we have implemented a new tool obthermo in the OpenBabel program suite including a table of reference atomization energy values for popular thermochemistry methods. This paper also provides predictions of Δ f H 0, S 0, and C V for well over 700 compounds for which no experimental data could be found in the literature. With the correction we find an RMSD from experiment of ≈13 J/mol K for 1273 compounds. This allows an empirical correction of the calculated entropy for molecules with multiple conformations. We observe that the deviation of composite quantum thermochemistry recipes from experimental S 0 corresponds roughly to the Boltzmann equation ( S = RlnΩ), where R is the gas constant and Ω the number of possible conformations.

This problem can be tackled in principle by performing thermochemistry calculations for all stable conformations, but this is not practical for large molecules. Quantum methods systematically underestimate S 0 for flexible molecules in the gas phase if only a single (minimum energy) conformation is taken into account. A large data set may help to evaluate quantum thermochemistry tools in order to uncover possible hidden shortcomings and also to find experimental data that might need to be reinvestigated, indeed we list and annotate approximately 200 problematic thermochemistry measurements. Large scale quantum calculations for molar enthalpy of formation (Δ f H 0), standard entropy ( S 0), and heat capacity ( C V) are presented.

Absolute entropy table