Capturing the elusive curve-crossing in low-lying states of butadiene with dressed TDDFT

TL;DR

This paper demonstrates that dressed TDDFT effectively captures curve-crossings involving double-excitation states in molecules, providing accurate energy surfaces and excitation characters crucial for modeling ultrafast molecular dynamics.

Contribution

The study introduces the use of frequency-dependent kernel of dressed TDDFT beyond Tamm-Dancoff to accurately model potential energy surface crossings involving double-excitation states.

Findings

Dressed TDDFT accurately predicts the energy surface near curve-crossings.

It successfully captures the double-excitation character of the dark 2$^1$Ag state.

Results are close to high-level $ ext{δ}$-CR-EOMCC(2,3) benchmarks.

Abstract

A striking example of the need to accurately capture states of double-excitation character in molecules is seen in predicting photo-induced dynamics in small polyenes. Due to the coupling of electronic and nuclear motions,the dark 2$^1$Ag state, known to have double-excitation character, can be reached after an initial photo-excitation to the bright $^1$Bu state via crossings of their potential energy surfaces. However, the shapes of the surfaces are so poorly captured by most electronic structure methods, that the crossing is missed or substantially mis-located. We demonstrate that the frequency-dependent kernel of dressed TDDFT beyond Tamm-Dancoff successfully captures the curve-crossing, providing an energy surface close to the highly accurate but more expensive $\delta$-CR-EOMCC(2,3) benchmark reference. This, along with its accurate prediction of the excitation character of the state makes dressed TDDFT a practical and accurate route to electronic structure quantities needed in modeling ultrafast dynamics in molecules.