Q: Why electronic excited states for diatomic molecules in #quantemolEC are represented differently than conventionally expected? For example, N2 molecule’s second and third excited states are represented by B1U, B3G instead of A 3∑u+, B 3∏g.
A: This is related to Group Theory. The quantum chemical packages employed in QEC only use D_{2h} symmetry and the subgroups of D2h. Because this is a diatomic molecule, which belongs to the D_\inf h point group, the calculation has to be carried out in the lower symmetry D2h group instead. That’s why the excited states are represented differently in the calculation results.
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