Modified enthalpies of formation for hydrocarbons from DFT and ab initio thermal energies

The enthalpies of formation of 50 selected hydrocarbon species have been calculated at different ab initio and density functional theory levels by applying the atomization energy approach. Comparing these values to reliable experimental data, the accuracy of theoretical methods were estimated. To analyze the relationship between the calculated and observed enthalpies of formation a three-parameter equation was used, to aim in minimizing the error of the calculations compared to the observed data. These parameters could be employed in estimating enthalpies of formation for similar molecular structures of larger size and those for which experimental data are rare. In addition, to calculate enthalpies of formation at any specific temperature, NASA polynomials were evaluated from computed heat capacities in the temperature range 300-1500 K.