= Solution
For conventional <CISD>, the leading matrix-vector contraction scales as $O(o^2v^4)$ in occupied and virtual orbital dimensions. If both grow proportionally to a system-size parameter $N$, the familiar estimate is \b[$O(N^6)$ work per iteration]; the iteration count and integral-storage strategy add implementation-dependent costs.
Calculated <potential energy surfaces> can predict equilibrium geometries and harmonic force constants, permitting comparison with diffraction-derived structures, <rotational constants> and vibrational spectra. Calculating several roots or different charge states can also estimate excitation or <ionization energies>. Such predictions depend on basis and truncation quality; truncated <CI> is not generally size extensive and is not automatically reliable for strongly multiconfigurational bond breaking. The quoted polynomial scaling is for <CISD>, not full <configuration interaction>, whose <determinant> space grows combinatorially.
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