Koopmans'-Type Theorem in Kohn-Sham Theory with Optimally Tuned Long-Range-Corrected (LC) Functionals.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Physics

Background:

• Kohn-Sham Density Functional Theory (KS-DFT) is a powerful tool for electronic structure calculations.
• Koopmans' theorem provides a theoretical basis for predicting ionization potentials (IP) from orbital energies.
• Standard KS-DFT methods often struggle with accurate IP predictions, especially for extended systems.

Purpose of the Study:

• To investigate the applicability of long-range-corrected (LC) functionals within the Kohn-Sham Koopmans'-type theorem framework.
• To evaluate the performance of optimally tuned LCgau-core functionals for calculating ionization potentials (IP).
• To assess the accuracy of this approach compared to established high-accuracy methods.

Main Methods:

• Employed optimally tuned LCgau-core functionals with BOP and PW86-PW91 exchange-correlation functionals.
• Calculated ionization potentials (IP) using a Kohn-Sham Koopmans'-type theorem approach.
• Optimized the range separation parameter (μ) for each molecular system to minimize the difference between negative HOMO energy and experimental IP.

Main Results:

• Optimally tuned LC functionals accurately predict ionization potentials (IP) for outer valence electronic levels.
• The accuracy of the LC-based Koopmans' method is comparable to highly accurate ab initio theories for outer valence IPs.
• The method shows reduced accuracy for inner valence and core electronic levels.

Conclusions:

• Orbitals derived from KS-DFT using LC functionals provide an accurate one-electron energy spectrum.
• This approach offers a simple yet effective one-electron orbital theory for electronic structure calculations.
• The method is practical and demonstrates significant utility in predicting ionization potentials.