A new arXiv preprint — not yet peer-reviewed — argues that the nontrivial topology surrounding molecular conical intersections (CIs) has dynamical consequences that go beyond the well-known Berry phase. Using the linear Jahn-Teller model as a testbed, the authors show that adding a Pauli σy term to the Hamiltonian can convert a CI into an avoided crossing while leaving the underlying topological character intact — a molecular analogue of manipulations familiar from condensed-matter physics.
Drawing on that analogy explicitly, the authors define a half-integer topological invariant as the integral of the Berry curvature over the nuclear branching space of the CI. They then test whether this invariant has physical consequences by running fewest-switches surface hopping simulations on eigensurfaces that are energetically identical but topologically distinct. The simulations reveal different hopping rates between the two cases, suggesting that topology — not just the shape of the potential energy surface — influences nonadiabatic dynamics.
If the results survive peer review, they would broaden the role of geometric and topological effects in photochemistry and molecular quantum dynamics, connecting concepts from topological band theory to the behavior of excited molecules undergoing internal conversion or intersystem crossing via spin-orbit coupling. The work remains a preprint and has not yet been independently validated.