Knowledge Bank

Effective core potentials for the Ar, Kr, and Xe atoms derived from numerical Hartree-Fock and Dirac-Hartree-Fock wave functions are applied in SCF and CI calculations of homonuclear diatomic potential energy curves. Detailed comparisons are made with the all electron calculations of Wadt for the ground and lowest positive ion states. Relativistic effects, excluding spin-orbit coupling, are seen to be unimportant for the three systems. Plots of the potential energy curves and computed molecular constants show excellent agreement with the all electron results. On the other hand, comparisons with results obtained using effective core potentials derived using varients of Phillips-Kleinman procedures show dramatic differences for $Xe2$ and $Xe2\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}$. SCF results for $Xe2$ and $Xe2\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}$ using $\omega -\omega$ coupling, which includes the spin-orbit term for tire core electrons, are shown to agree well with those obtained by including the spin-orbit effects using an empirical procedure.