On the functional dependence of transition-potential coupled cluster

Area of Science:

• Quantum Chemistry
• Computational Spectroscopy
• Electronic Structure Theory

Background:

• Core ionization and excitation energies are crucial in spectroscopy but often suffer from computational errors due to orbital relaxation.
• Transition-Potential Coupled Cluster (TP-CC) methods offer a way to explicitly address orbital relaxation by using fractionally occupied orbitals.

Purpose of the Study:

• To evaluate the impact of various density functionals on the accuracy of TP-CC calculations for core-level spectroscopy.
• To determine if the choice of functional for generating fractionally occupied orbitals affects the reliability of TP-CC results.

Main Methods:

• Employed Transition-Potential Coupled Cluster (TP-CC) methods, specifically TP-CCSD and XTP-CCSD.
• Utilized fractionally occupied orbitals generated by several density functionals (HF, BP86, BH&HLYP, B3LYP, M06-2X, ωB97m-V).
• Calculated organic K-edge x-ray absorption and photoelectron spectra.

Main Results:

• TP-CC calculations produced accurate and comparable core ionization energies, core excitation energies, and oscillator strengths across all tested density functionals.
• The choice of functional for generating the initial fractionally occupied orbitals did not significantly impact the final TP-CCSD results.

Conclusions:

• Density functional choice for generating fractionally occupied orbitals has minimal impact on the accuracy of TP-CC calculations for K-edge spectra.
• TP-CC methods provide robust and reliable computational tools for core-level spectroscopy, irrespective of the preceding functional choice.