Determination of the standard enthalpy of formation of iodine compounds through the G2 and G3(MP2)//B3-SBK theories.

The domain of application of the G3(MP2)//B3-SBK theory was expanded, and its efficiency was evaluated to determinate enthalpies of formation of forty-one iodine compounds. The results were compared to those obtained with the G2 theory for the same set of molecules. The G3(MP2)//B3-SBK theory showed a mean deviation and deviation standard equal to 3.7 kcal mol-1 and 6.0 kcal mol-1, respectively. The G2 theory (mean deviation = 3.1 kcal mol-1 and standard deviation = 4.9 kcal mol-1) presented a lower error and standard deviation, but at a significantly higher computational cost. For a more complete evaluation, as a secondary part of the work, it also used different functionals B3LYP, M06-2X, WB97XD, and MP2 method with four different basis sets 6-311G(d,p), LANL2DZ, jorge-ADZP, and CEP-31G(d). The best density functional/basis set combination was obtained with M06-2X/CEP-31G(d) among the three mentioned functionals. However, the produced mean deviation is significant and equal to 17.3 kcal mol-1, with a standard deviation equal to 23.0 kcal mol-1. The 6-311G(d,p) basis achieved the best performance with the MP2 method, generating an equally significant mean deviation of 12.8 kcal mol-1 with a standard deviation equal to 18.7 kcal mol-1.