Hole-hole Tamm-Dancoff-approximated density functional theory: A highly efficient electronic structure method...

Area of Science:

• Computational chemistry
• Theoretical chemistry
• Photochemistry

Background:

• Accurate electronic structure methods are vital for studying photochemical reaction dynamics.
• Time-dependent density functional theory (TDDFT) struggles with static correlation, while complete active space self-consistent field methods neglect dynamic correlation.
• There is a need for cost-effective methods that capture both static and dynamic electron correlation.

Purpose of the Study:

• To revisit and evaluate the hole-hole Tamm-Dancoff approximated (hh-TDA) density functional theory for photochemical applications.
• To assess hh-TDA's capability in describing ground and excited states, including conical intersections.
• To investigate the inclusion of dynamic correlation within the hh-TDA framework using density functional approximations.

Main Methods:

• Utilizing the hole-hole Tamm-Dancoff approximated (hh-TDA) method, derived from particle-particle random phase approximation (pp-RPA).
• Obtaining N-electron states via double annihilations from a doubly anionic (N+2 electron) reference state.
• Employing functional-dependent response kernels in hh-TDA, similar to linear response and collinear spin-flip TDDFT.

Main Results:

• hh-TDA treats ground and excited states on equal footing, enabling correct description of conical intersections.
• The method incorporates dynamic correlation through standard density functional approximations.
• hh-TDA shows promise for efficiently treating photochemistry in organic and biochemical systems, especially those with low-lying ππ* and nπ* states.

Conclusions:

• hh-TDA is a computationally efficient method for photochemical reaction dynamics.
• It accurately captures essential static and dynamic electron correlation effects.
• This method is particularly suitable for complex systems involving multiple excited states where dynamic correlation is critical.