Beyond Spin Models in Orbitally Degenerate Open-Shell\nNanographenes

The study of open-shell\nnanographenes has relied on a paradigm\nwhere spins are the only low-energy degrees of freedom. Here we show\nthat some nanographenes can host low-energy excitations that include\nstrongly coupled spin and orbital degrees of freedom. The key ingredient\nis the existence of orbital degeneracy, as a consequence of leaving\nthe benzenoid/half-filling scenario. We analyze the case of nitrogen-doped\ntriangulenes, using both density-functional theory and Hubbard model\nmulticonfigurational and random-phase approximation calculations.\nWe find a rich interplay between orbital and spin degrees of freedom\nthat confirms the need to go beyond the spin-only paradigm, opening\na new avenue in this field of research.