Ab initio nonadiabatic coupling elements: the conical intersection between the three lower states of the {H2O} system

In this numerical treatment efforts were made to reveal the conical intersections (ci) between the two lower, 12A′ and 22A′ states – to be designated as (1,2) ci – and the (2,3) cis between the two upper, 22A′ and 32A′ states – of the {H2O} system. We found that the two lower states are coupled by cis located along the O–H–H and the H–O–H arrangements. No other arrangement was found to form (1,2) cis. As for the (2,3) cis, they are found to be C2v cis located along the symmetry line that connects the center-of-mass of the two hydrogens and the oxygen.