Conical intersections in 22E′ states of Na3 cluster

►We calculate PESs and Non-Adiabatic Coupling Terms by ab initio method on the excited states of Na3. ► Four conical intersections (CIs) in 22E′ states are suspected from Non-Adiabatic Coupling Terms. ► Adiabatic to Diabatic transformation matrix elements' (diagonal) sign changes are observed. ► Longuet-Higgins' sign flip is demonstrated in order to confirm the existence of four CIs.