Pragmatic Approach to Photodynamics: Mixed Landau-Zener Surface Hopping with Intersystem Crossing.

Ab initio excited state photodynamical simulations have entered the mainstream in the past two decades, bringing techniques of various sophistication and computational requirements for the description of nonadiabatic transitions. We explore in this work the performance of the recently reformulated Landau-Zener surface hopping (LZSH) approach and extend it for the simultaneous treatment of internal conversion and intersystem crossing events. We studied photochemical reactions of four model molecules (cyclopropanone, methaniminium cation, cytosine, and thiophene). The calculated quantities are generally in excellent agreement with the corresponding fewest switches surface hopping simulations. Furthermore, the algorithm proved to be significantly more stable and more computationally efficient. LZSH also puts fewer constraints on the electronic structure theory as the nonadiabatic couplings are not needed. We argue that the accuracy of photodynamical simulations is in practice dominated by the electronic structure theory, and it is, therefore, legitimate to use the simplest and the most efficient technique for the treatment of nonadiabatic transitions.