Ensemble density variational methods with self- and ghost-interaction-corrected functionals.

Area of Science:

• Quantum Chemistry
• Computational Physics
• Theoretical Chemistry

Background:

• Ensemble density functional theory (DFT) offers a method for calculating excited-state energies of atomic and molecular systems.
• Practical applications and reliable assessments of ensemble DFT approximations have been limited.
• Existing approximations may suffer from self-interaction and ghost-interaction errors.

Purpose of the Study:

• To investigate and compare two ensemble DFT functional forms: the Gross, Oliveira, and Kohn (GOK) functional and the orbital-dependent eDFT functional.
• To address and correct self-interaction and ghost-interaction errors in approximate ensemble density functionals.
• To evaluate the accuracy of these functionals for predicting excitation energies.

Main Methods:

• Formulation of ensemble density functionals within the ensemble DFT framework.
• Employment of local and semi-local ground-state density functionals.
• Development of corrections for self-interaction and ghost-interaction in the GOK functional.
• Numerical applications and comparison of the GOK and eDFT functional performances.

Main Results:

• The eDFT functional, inherently free of ghost-interaction, yields significantly more reliable results compared to approximate self- and ghost-interaction-corrected GOK functionals.
• Approximate ensemble density functionals can contain spurious self-interaction and ghost-interaction errors.
• Self-interaction corrected local density functionals within the eDFT framework achieve accuracy comparable to uncorrected semi-local eDFT functionals.

Conclusions:

• The eDFT functional approach is more robust for calculating excited-state energies due to its construction free of ghost-interaction.
• Corrections for self- and ghost-interactions in the GOK functional do not fully resolve the inaccuracies.
• Ensemble DFT, particularly the eDFT formulation, shows significant promise for accurate excited-state energy predictions in quantum systems.