Approaching chemical accuracy with density functional calculations: Diatomic energy corrections

Density functional theory (DFT) is widely used to predict materials properties, but the local density approximation (LDA) and generalized gradient approximation (GGA) exchange-correlation functionals are known to poorly predict the energetics of reactions involving molecular species. In this paper, we obtain corrections for the O₂, H₂, N₂, F ₂, and Cl₂ molecules within the Perdew-Burke-Enzerhof GGA, Perdew-Wang GGA, and Perdew-Zunger LDA exchange-correlation functionals by comparing DFT-calculated formation energies of oxides, hydrides, nitrides, fluorides, and chlorides to experimental values. We also show that the choice of compounds used to obtain the correction is significant, and we use a leave-one-out cross-validation approach to rigorously determine the proper fit set. We report confidence intervals with our correction values, which quantifies the variation caused by the choice of fit set after outlier removal. The remaining variation in the correction values is of the order of 1 kcal/mol, which indicates that chemical accuracy is a realistic goal for these systems.