New Framework for Multi-Electronic-State Dynamics and Its Validation for Photoisomerization of 1,3-Cyclohexadiene

intersections, and ring-opening quantum yields of 43-53%. ODM3.25-SRP enables nonadiabatic dynamics of cyclohexadiene with XMS-CASPT2 quality and an expanded active space while reducing the computation time by a factor of 65. This work demonstrates that treating ODM3.25 as a domain-specific foundation model and fine-tuning it via SRP yields a computationally efficient, chemically accurate multistate potential capable of describing complex photodynamics at a fraction of the cost of high-level ab initio methods. This establishes SRP-based custom excited-state models as a powerful new tool for large-scale nonadiabatic dynamics.