Extension of complete basis set model chemistries to molecules containing third row atoms Ga-Kr

The complete basis set methods, CBS-4, CBS-q, CBS-Q and CBS-QB3, have been extended to molecules containing the third row elements Ga-Kr and their performance is assessed on 40 energies (atomization energies, ionization energies, electron affinities, and proton affinities) from the third row G2 test set. The mean absolute deviation from experiment for the highly accurate methods, CBS-Q and CBS-QB3, are 1.15 kcal/mol and 1.12 kcal/mol, respectively, both lower than for the G2 method, but not as low as the G3 method. The mean absolute deviation from experiment for the more affordable methods, CBS-4 and CBS-q, are 2.23 kcal/mol and 1.81 kcal/mol, respectively. The set of methods, CBS-4(d), CBS-q(d), CBS-Q(d), and CBS-QB3(d), with the d orbitals included in the correlation space is also investigated, giving results in poorer agreement with experiment. Problems with the CBS extrapolation step when the d orbitals are included in the correlation space are also discussed. (C) 2003 American Institute of Physics.