Conical intersections control excited state reactivity, and understanding the electronic structure around them is crucial for photochemistry studies. To locate these intersections one needs accurate and efficient electronic structure methods. In contrast to the most accurate methods (e.g. XMS-CASPT2) which are computationally intractable for large molecules, the state-interaction state-averaged restricted ensemble averaged Kohn-Sham (SI-SA-REKS) method is a computationally efficient alternative. However, its application in photochemistry used to be hampered by the lack of analytical nuclear gradients and non-adiabatic coupling matrix elements. Here we derived the analytical energy derivatives formalism for SI-SA-REKS method and implemented the method effectively on graphical processing units (GPUs). We demonstrate that our implementation gives the correct topography and energetics of the conical intersection, and is computationally efficient with a scaling of O(N<sup>1.77</sup>), making it capable of investigating excited state dynamics of large molecular systems.

Exploiting graphical processing units to enable accurate excited state potential energy surface calculation for large molecules

255th National Meeting (2018)

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