Excited state molecular dynamics on potential energy surfaces associated with individual electronic energy eigenstates is an important concept that spurred the first era of <i>ab initio </i>simulations of photophysical processes.  However, for many applications of technological interest (photovoltaic/light-emitting materials, photocatalysis, information processing, etc.) it becomes mandatory to consider the explicit time evolution of the electronic state of the system to achieve a qualitatively correct description of the underlying excited state processes.  Through explicit propagation of the electronic state, the constraint of adiabatic evolution is lifted and the time-dependence of populations/coherences of excited and ground electronic states can be modeled from first principles.  When the spin-free, non-relativistic Hamiltonian is employed, internal conversion and vibrational relaxation processes are captured.  However, relativistic Hamiltonians that naturally account for spin-orbit coupling are needed to simulate processes for which spin angular momentum is not a conserved quantity.  In the exact two component formulation of the relativistic electronic Hamiltonian presented here, spin-orbit and spin-spin interactions can be selectively included, providing a mechanism to disentangle the specific driving forces behind different spin-forbidden processes.  In this contribution, the experimentally-observed excited state intersystem crossing following impulsive excitation of a coherent superposition of low-lying valence excited states in a binuclear Platinum complex is considered as case study where spin-forbidden processes and excited state coherence effects both naturally manifest.           <br/>

Modeling excited-state intersystem crossing with relativistic time-dependent electronic structure theory

256th National Meeting (2018)

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