Dual-Functional Tamm-Dancoff Approximation: A Convenient Density Functional Method that Correctly Describes S₁/S₀ Conical Intersections.

Accurate non-adiabatic dynamics simulations require sophisticated electronic structure theories that can describe the complex wavefunctionsin different regions of the potential energy surfaces (PESs). Conical intersections (CIs), facilitating the population transfer from one state to the other, play an important role in the non-adiabatic processes. Hence, efficient and accurate electronic structure theories should correctly describe the double cone topology of the PESs near CI. The current theories that can correctly describe the CI regions of the PESs are mostly based on the multi-reference methods. However, the computational cost of the multi-reference methods grows exponentially when the active space increases. On the other hand, LR-TDDFT is both efficient and accurate but unable to describe the CIs between ground and excited states. Hence the applications of LR-TDDFT in the non-adiabatic processes are limited. In this presentation, we introduce a novel theoretical method based on LR-TDDFT, named dual functional Tamm-Dancoff approximation that can describe the correct topology of the PESs near CI and can be accurate as LR-TDDFT.