Energy-Specific Linear Response TDHF/TDDFT for Calculating High-Energy Excited States

An energy-specific TDHF/TDDFT method is introduced in this article for excited state calculations. This approach extends the conventional TDHF/TDDFT implementation to obtain excited states above a predefined energy threshold. The method introduced and developed in this work enables computationally efficient yet rigorous calculations of energy-specific spectra, e.g., X-ray absorption involving extremely high-energy transitions. All transitions are solved in the full molecular orbital space, and orthogonality to the ground state and lower-lying excited states is preserved for each high-energy excited state. Encouraging computational savings are observed in calculating the targeted energy spectrum, while the transition energies, as well as oscillator strengths, remain identical to the results from the standard implementation.