External orthogonality in subsystem time-dependent density functional theory.

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Materials Science

Background:

• Subsystem density functional theory (DFT) offers a partitioning approach to quantum chemical calculations.
• Approximations to the kinetic energy density functional (KEDF) limit the accuracy of traditional subsystem DFT methods.
• External orthogonality (EO) provides a way to circumvent KEDF approximations by enforcing inter-subsystem molecular orbital orthogonality.

Purpose of the Study:

• To extend an existing subsystem DFT method incorporating external orthogonality (EO) into the time-dependent DFT (TDDFT) framework.
• To eliminate the necessity for approximate kinetic energy potentials and kernels in TDDFT calculations.
• To validate the accuracy of the developed method against supermolecular TDDFT results.

Main Methods:

• Development of a novel time-dependent subsystem DFT (TD-subsystem DFT) method.
• Incorporation of external orthogonality (EO) to ensure exactness in principle.
• Application of the TD-subsystem DFT-EO method to systems with varying degrees of subsystem coupling and density overlap.

Main Results:

• The TD-subsystem DFT-EO method accurately reproduces supermolecular TDDFT results.
• The method demonstrates reliability for both weakly and strongly coupled subsystems.
• Effective reproduction of results for systems with significant density overlap, a challenge for traditional KEDF approximations.

Conclusions:

• The developed TD-subsystem DFT-EO method offers an accurate and robust alternative to traditional TDDFT approaches.
• This method removes the reliance on approximate KEDFs, enhancing the reliability of electronic structure calculations.
• The approach shows significant promise for studying complex molecular systems where KEDF approximations falter.