Derivative Couplings between Time-Dependent Density Functional Theory Excited States in the Random-Phase...

Area of Science:

• Computational chemistry
• Quantum chemistry
• Theoretical chemistry

Background:

• Derivative couplings are essential for describing non-adiabatic molecular dynamics.
• Accurate calculation of derivative couplings is computationally challenging.
• Conical intersections are critical points in excited-state potential energy surfaces.

Purpose of the Study:

• To present a novel formalism for derivative couplings between time-dependent density functional theory (TD-DFT) excited states.
• To implement this formalism within the random-phase approximation (RPA) using analytic gradient theory.
• To validate the formalism by checking its ability to recover known properties around conical intersections.

Main Methods:

• Development of a pseudo-wavefunction approach for derivative couplings.
• Application of analytic gradient theory within the random-phase approximation (RPA).
• Validation against finite-difference overlaps and known properties at conical intersections.

Main Results:

• A robust formalism for calculating derivative couplings between TD-DFT excited states was established.
• The method correctly reproduces the behavior of derivative couplings near conical intersections.
• The formalism was successfully applied to the test case of protonated formaldimine (CH2NH2(+)).

Conclusions:

• The presented formalism provides an accurate and efficient way to compute derivative couplings.
• This work is crucial for reliable simulations of excited-state dynamics and photochemical reactions.
• The method lays the groundwork for further investigations into non-adiabatic processes.