The FO2 radical: a new success of density functional theory

The structure, heat of reaction and heat of formation of the FO2 radical in its X2A″ ground state has been calculated using the three-parameter exchange functional of Becke and the Lee-Yang-Parr functional for correlation energy (B3LYP method). B3LYP geometrical parameters of FO2 and FO are nearer to experiment than those obtained with conventional ab initio calculations. The calculated ΔHr,00 for F + O2 → FO2 at this level (−11.1 kcal/mol) is nearer to experiment (−11.68 kcal/mol) than that afforded by any other calculation, including QCISD(T), MP4(SDTQ) or G1 ab initio models. Calculation of the heat of reaction for previously considered isodesmic and isogyric reactions involving the FO2 radical shows that the agreement is consistent. The root mean square error for the sixteen reactions considered, involving FO, FO2, FOH and FOOF, with heats of reaction varying from -149 to +56 kcal/mol, is 0.5 kcal/mol at the B3LYP level. The similar rms error for MP4(SDTQ)/6-311+ +G(2d, 2p) calculations is 5.2 kcal/mol. It is concluded that the B3LYP method is faster and more accurate than conventional ab initio methods for the study of reactions involving F-O bonds.