What happens to a molecule once it has absorbed UV or visible light? How does the molecule release or convert the extra-energy it just received? Answering these questions clearly goes beyond a pure theoretical curiosity, as photochemical and photophysical processes are central for numerous domains like energy conversion and storage, radiation damages in DNA, or atmospheric chemistry, to name a few. Ab initio multiple spawning (AIMS) is a theoretical tool that aims at an accurate yet efficient in silico description of photochemical and photophysical processes in molecules. AIMS describes the excited-state dynamics of nuclear wavepackets using adaptive linear combinations of traveling frozen Gaussians [1].

In this talk, I intend to survey some recent developments and applications of the AIMS technique. A significant feature of the AIMS framework – besides its controlled approximations [2,3] – is its adaptability, which permits the addition of critical physical processes for a realistic simulation of photochemical processes. For example, we recently included spin-orbit coupling in AIMS [4] and the effect of an external electric field [5], leading to two new schemes called Generalized AIMS (GAIMS) and eXternal Field AIMS (XFAIMS). We also proposed a simple yet rational approximation to AIMS termed Stochastic-Selection AIMS (SSAIMS), which allows decreasing the computational cost of an AIMS dynamics substantially [6].

Also, we also interfaced AIMS with the GPU-based electronic structure code TeraChem to study the excited-state dynamics of large molecular systems. Combining the accuracy of AIMS with the efficiency of GPU-accelerated electronic structure calculations (LR-TDDFT or SA-CASSCF) allows indeed for a significant step forward in the simulation of nonadiabatic events, as it pushes the boundaries of the well-known compromise between efficiency and accuracy imposed by the computational cost of such dynamics. Thanks to this new interface, we could investigate the nonadiabatic dynamics of different medium-size organic molecules important in biological chemistry, organic electronics, and atmospheric chemistry [7-9].

[1] B. F. E. Curchod and T. J. Martínez, Chem. Rev.,2018, 118, 3305.
[2] B. Mignolet and B. F. E. Curchod, J. Chem. Phys.,2018, 148, 134110.
[3] B. Mignolet and B. F. E. Curchod, J. Phys. Chem A, 2019, 123, 3582.
[4] B. F. E. Curchod, C. Rauer, P. Marquetand, L. González, and T. J. Martínez, J. Chem. Phys.,2016, 144, 101102.
[5] B. Mignolet, B. F. E. Curchod, and T. J. Martínez, J. Phys. Chem.,2016, 145, 191104.
[6] B. F. E. Curchod, W. J. Glover, and T. J. Martínez, in preparation,2018.
[7] J. W. Snyder Jr., B. F. E. Curchod, and T. J. Martínez, J. Phys. Chem. Lett.,2016, 7, 2444.
[8] B. Mignolet, B. F. E. Curchod, and T. J. Martínez, Angew. Chem. Int. Ed.,2016, 55, 14993.
[9] B. F. E. Curchod, A. Sisto, and T. J. Martínez, J. Phys. Chem. A,2017, 121, 265.