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High-Quality Thermochemistry Data on Polycyclic Aromatic Hydrocarbons via Quantum Chemistry

In this article, recent work on calculating high-quality enthalpies of formation for polycyclic aromatic hydrocarbons (PAHs) based on both density functional theory (DFT) and Gaussian-3 (G3) model chemistry methods is discussed. It is shown that through the use of an empirical correction model, the systematic errors in low-level DFT calculations can be controlled to produce reliable thermochemistry. It is further shown that the G3 results have a more regular systematic error and as a consequence a simpler model may be used to correct for systematic deviations. It is seen that the resulting enthalpy of formation values are in good agreement with the available experimental data, and that the predictions are sufficiently robust to point out certain errors in experimental determinations. This work was done as part of a larger effort to create a curated data set of property data for a large set of PAH molecules. In furtherance of this goal, UV/Vis spectra have been computed using time-dependent DFT. The collection of PAH data is being made publicly available through a web-based database that is briefly described.