Knowledge Bank

MCSCF-CI and NO-CI potential curves have been computed for the lowest-lying $X1\Sigma +,A1\Sigma +,a3\Pi ,A\prime 1\Pi$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma +$ states of CaO. At this writing, second-order type NO-CI calculations have been carried out for $X1\Sigma +$. The second-order curves differ from the first-order curves reported last year at this meeting. The major difference is that the second order curves do not exhibit the slight bump near $Re$ which appears in the first-order curves. Analysis indicates that the extensive interaction between $X1\Sigma +$ and $A1\Sigma +$ near $Re$ is responsible for the difference between the first-order and second-order results. This interaction is manifest in the rapidly changing character of the electronic wavefunction, and, roughly speaking is associated with the change of configuration $Ca2+O2-\to Ca1+O1-$. Extensively correlated wavefunctions are required to characterize this configuration change.