According to the molpro manual, section 7.3:

In order to compute excited states it is usually best to optimize the energy average for all states under consideration. This avoids root-flipping problems during the optimization process and yields a single set of compromise orbitals for all states.

Is see that SA-CASSCF is quite standard in the literature, even in cases when root-flipping wouldn't necessarily cause an issue, and I don't understand why making such compromise to obtain a single set of orbitals makes theoretical sense. Isn't it better to find the set of orbitals and the CI vector that minimizes the energy for each of the roots of interest?

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    $\begingroup$ Sorry, I never used that method so do not take my comments seriously. What you wrote seems reasonable to me, I bet it depends on what will you do with those results. I hear that the states provided by that method are orthogonal to each others, which could be advantageous for someone. $\endgroup$ May 2, 2019 at 21:00
  • $\begingroup$ The answer is given in my paper of over 40 years ago. Josip Hendekovic, On the energy variation method, Chem. Phys. Letters 90,(1982) 198. Two new theorems are proved, specifically with excited states in mind. On request I will send a copy! $\endgroup$ Dec 24, 2023 at 21:49


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