Theoretical Study on the Intersection Structures between Potential Energy Surfaces

The crossing of potential energy surfaces plays an important role in photo-decay processes and photochemical reactions. The energies and geometries of the crossing points have been reported for various molecules using quantum chemical calculations. In this research, excitation energy components of uracil are investigated to understand the characteristics of the crossing points. We revealed that the HOMO-LUMO exchange integral becomes approximately zero at the minimum energy conical intersection between S-0 and S-1 states. Furthermore, it was found that the HOMO - LUMO gap is close to the HOMO-LUMO Coulomb integral at the crossing structures.