Development of constrained multicomponent time-dependent density functional theory for incorporation of nuclear quantum effects in electronic excited state calculations

Nuclear quantum effects play a significant role in a variety of excited state processes. However, the incorporation of nuclear quantum effects in electronic excited state calculations has been highly challenging. To address this challenge, we develop the constrained multicomponent time-dependent density functional theory with the frozen nuclear orbital approximation. We apply the new theory to the calculation of vibrational frequencies of a series of molecular systems and observe significant improvement over the conventional time-dependent density functional theory in predicting the frequencies for modes with significant hydrogen motion. The new theory is promising for simulating excited state dynamics with strong nuclear quantum effects, such as excited state proton transfer reactions.