Probing Basis Set Requirements for Calculating Core Ionization and Core Excitation Spectra Using Correlated Wave...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate calculation of core excitations and ionizations is crucial in various chemical and physical processes.
• Existing basis sets may not be optimal for describing core electronic states using advanced correlated wave function methods.

Purpose of the Study:

• To investigate the basis set requirements for accurate core excitation and ionization calculations.
• To develop and propose a new hierarchical sequence of basis sets for core excitation calculations.

Main Methods:

• Employed correlated wave functions of coupled cluster type.
• Utilized linear response methods for describing core excitations.
• Systematically studied basis set sensitivity for atoms B-Ne.

Main Results:

• Density functional theory (DFT) approaches for core excitations allow for balanced basis set tailoring.
• Coupled cluster linear response methods necessitate a different, more extensive basis set, including s- and p-type functions and core polarization functions.
• The proposed ccX-nZ basis set series demonstrates lower basis set errors compared to existing sets for a given size.

Conclusions:

• The ccX-nZ basis sets are recommended for accurate core excitation calculations using correlated wave function linear response and equation-of-motion methods.
• These basis sets provide a more accurate description for core electronic processes.
• For large systems, mixed basis sets combining ccX-nZ with standard sets can be used, though accuracy may vary.