Fig. 4

TTNS simulation of singlet fission in DP-Mes and structural experimental comparison. a Schematic of TTNS. The electronic system is coupled to 252 vibrational modes (ω) in DP-Mes. By means of entanglement renormalisation, a tree of linearly connected vibrational modes connected to the electronic system via entanglement renormalisation nodes (blue) can be created, allowing facile computation of non-Born-Oppenheimer dynamics for large molecules (>100 atoms, further details in Methods). The vibrational modes are grouped by symmetry and colour coded to indicate tuning (orange) or coupling (green) mode behaviour. b Projected total time-dependent mode displacements for all symmetry groups and their corresponding assignment. We remark the ~200-fold lower displacement amplitude for A₂, B₁ and B₂ modes compared with the A₁ modes. c S₁ → ¹TT coherence transfer Raman spectrum (blue) and resonance Raman representation of the calculated spectrum (orange). d Intrinsic ¹TT Raman spectrum (purple) compared with the resonance Raman representation of calculations initiated in ¹TT (orange). Calculated modes marked with an asterisk in (c) and (d) are not detected in the experimental spectrum, likely due to resonance Raman enhancement effects