Revisiting the ring-opening mechanisms of oxirane using time-dependent GW molecular dynamics

Oxirane (ethylene oxide, C₂H₄O) is a prototypical three-membered ring system whose ultraviolet (UV) induced ring-opening has long served as a model for understanding bond dissociation on excited-state surfaces. Upon photoexcitation, oxirane undergoes ultrafast C–O bond cleavage followed by intramolecular rearrangements to yield products such as CH₄, C₂H₄, CO, and H. Previous computational studies using time-dependent density functional theory molecular dynamics (TDDFT-MD) or constrained-density functional theory molecular dynamics (c-DFT-MD) attempted to elucidate the mechanisms of these products but relied on the adiabatic local density approximation (ALDA), which is well-known to be unsuitable for initially excited states. In this talk, I revisit the ring-opening process in oxirane using our newly developed time-dependent GW molecular dynamics (TDGW-MD) method [J. Chem. Phys. 160, 184102 (2024)], a first-principles approach applicable to excited states. I present pathways following Kasha’s rule (excited states involving HOMO) and alternative channels via higher excited states (involving HOMO–1) accessible under UV excitation. These results highlight TDGW-MD as a promising route for accurate excited-state dynamics at a reasonable computational cost.