Ascertain prevalence and significance of SS-CASSCF irregularities in larger molecules and basis sets

Ascertain the prevalence and significance of coalescence, disappearance, and other irregularities in state-specific CASSCF excited-state solutions for larger molecules and basis sets relevant to photochemistry, in order to enable a firm evaluation of the long-term viability of SS-CASSCF.

Background

The authors identify irregularities in state-specific solutions, such as pair annihilation and fold catastrophes, which can lead to discontinuities in potential energy surfaces and hinder dynamic simulations.

While the study characterizes such behavior for ethylene, the broader prevalence and impact of these irregularities across larger systems and photochemical basis sets remain undetermined, posing a key question for the practical adoption of SS-CASSCF in computational photochemistry.

References

However, the prevalence and significance of these irregularities for excited energy surfaces in larger molecules and basis sets of photochemical interest remain to be determined, preventing a firm evaluation of the long-term viability of SS-CASSCF theory.

— Excited state-specific CASSCF theory for the torsion of ethylene  (2402.13046 - Saade et al., 2024) in Section 1 (Introduction)