Density functionals for core excitations.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate prediction of molecular electronic structure is crucial for understanding chemical phenomena.
• Density functional theory (DFT) and equation-of-motion coupled cluster (EOM-CC) are key computational methods.
• Core excitation and ionization energies provide insights into electronic structure and bonding.

Purpose of the Study:

• To evaluate the performance of various density functionals in calculating core excitation and ionization energies.
• To compare DFT results with benchmark EOM-CC calculations.
• To identify accurate and efficient DFT methods for core-level spectroscopy predictions.

Main Methods:

• Calculation of core excitation and ionization energies using multiple density functionals.
• Application of both time-dependent and time-independent formulations within DFT and EOM-CC.
• Comparison of calculated values against established EOM-CC benchmark data.

Main Results:

• The QTP(00) functional, parameterized using only water's ionization potentials, demonstrated excellent accuracy for core excitation and ionization energies.
• The QTP(00) functional consistently outperformed other tested functionals.
• Orbital eigenvalues from Kohn-Sham (KS) DFT were identified as significant factors influencing spectral accuracy.

Conclusions:

• The QTP(00) functional presents a highly accurate and efficient method for predicting core-level electronic properties.
• KS-DFT orbital eigenvalues are critical determinants for the precision of excitation and photoelectron spectra.
• This work provides a valuable tool for researchers in computational and theoretical chemistry.