Molecular π-Orbital Construction for Non-Planar Conjugated Systems.

We extend the π-orbital space (PiOS) method introduced for planar π-conjugated molecular systems [ J. Chem. Theory Comput. 2019 , 15, 1679] to also allow constructing efficient π-orbital active spaces for non-planar π-conjugated systems. We demonstrate the performance of this method with multiconfigurational and multireference calculations on prototypical non-planar π-systems: cycloacenes, short carbon nanotubes, various conformations of the 2,2 - bipyridine anion, and C 20 fullerenes.