Assessment of G3(MP2)∕∕B3 theory including a pseudopotential for molecules containing first-, second-, and third-row representative elements.

G3(MP2)∕∕B3 theory was modified to incorporate compact effective potential (CEP) pseudopotentials, providing a theoretical alternative referred to as G3(MP2)∕∕B3-CEP for calculations involving first-, second-, and third-row representative elements. The G3∕05 test set was used as a standard to evaluate the accuracy of the calculated properties. G3(MP2)∕∕B3-CEP theory was applied to the study of 247 standard enthalpies of formation, 104 ionization energies, 63 electron affinities, 10 proton affinities, and 22 atomization energies, comprising 446 experimental energies. The mean absolute deviations compared with the experimental data for all thermochemical results presented an accuracy of 1.4 kcal mol(-1) for G3(MP2)∕∕B3 and 1.6 kcal mol(-1) for G3(MP2)∕∕B3-CEP. Approximately 75% and 70% of the calculated properties are found with accuracy between ±2 kcal mol(-1) for G3(MP2)∕∕B3 and G3(MP2)∕∕B3-CEP, respectively. Considering a confidence interval of 95%, the results may oscillate between ±4.2 kcal mol(-1) and ±4.6 kcal mol(-1), respectively. The overall statistical behavior indicates that the calculations using pseudopotential present similar behavior with the all-electron theory. Of equal importance to the accuracy is the CPU time, which was reduced by between 10% and 40%.