Role of electron correlation in femtosecond relaxation of photoexcited electrons in C$_{\mathrm{60}}$

Electron-phonon coupled dynamics in molecules underpins many vital phenomena in matter, including the mobility and collection of carriers in organic devices [1]. Following the absorption of photons by a fullerene molecule, the relaxation of excited electrons to the band-edge via electron-phonon (e-p) coupling, transferring energy to the vibrational degrees of freedom, is of fundamental interest [2]. We simulate the relaxation dynamics in C$_{\mathrm{60}}$ using two schemes: (i) Quantum Espresso software to describe the structure and the PYXAID package, which employs classical trajectory surface hopping for non-adiabatic (NA) e-p coupling [3], to describe the dynamics; this is effectively a single particle frame. (ii) Electronic structure calculated with the package GAMESS, describing the ground state at the Hartree-Fock level and the excited states at the Configuration Interaction Singles (CIS) level, followed by surface-hopping NA dynamics using Chemical Dynamics Tool Kit [4]. Comparisons indicate a dramatically faster decay induced by correlations. Such ab initio results will motivate and complement femtosecond measurements of relaxation processes in fullerenes via RABITT and streaking approaches. [1] Coropceanu et al, Chem. Rev. \textbf{107}, 926 (2007); [2] Ross et al, Nature Materials \textbf{8}, 208 (2009); [3] Madjet et al, Phys. Chem. Chem. Phys. \textbf{18}, 5219 (2016); [4] Madjet et al., J. Chem. Phys. \textbf{138}, 094311 (2013).