EXTENSION OF GAUSSIAN-2 (G2) THEORY TO MOLECULES CONTAINING 3RD-ROW ATOMS K AND CA

Gaussian-2 (G2) theory has been extended to molecules containing the t hird-row nontransition elements K and Ca. Basis sets compatible with t hose used in G2 theory for molecules containing first-and second-row a toms, as well as the third-row elements Ga-Kr, have been derived. As f or Ga-Kr, first-order spin-orbit corrections are included explicitly i n the G2 energies of K-and Ca-containing atoms and molecules. In contr ast to the procedure for Ga-Kr, the 3s and 3p orbitals need to be incl uded in the cell-elation space for K-and Ca-containing molecules. The geometries obtained with the new basis sets are in satisfactory agreem ent with experiment. Assessment of the thermochemical predictions is l imited because of the sparsity of accurate experimental data for molec ules containing K and Ca, Ionization energies are generally in good ag reement with experimental values, as are the atomization energies for K-containing molecules. However. there are larger differences between theoretical and experimental atomization energies for Ca-containing mo lecules. (C) 1997 American Institute of Physics.