Basis Set Selection for Molecular Core-Level GW Calculations.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• The GW approximation is increasingly used for simulating molecular core-level X-ray photoemission spectra.
• Traditional methods using cc-pVnZ or def2-nZVP basis sets with extrapolation and relativistic corrections were thought to underestimate binding energies.

Purpose of the Study:

• To investigate the accuracy of GW approximation for core-level binding energies.
• To evaluate the convergence properties of different basis set families.
• To identify basis sets that provide accurate and efficient calculations for both core and valence electronic properties.

Main Methods:

• Calculations of core-level binding energies using the GW approximation.
• Systematic study of basis set convergence using standard (cc-pVnZ, def2-nZVP) and specialized (uncontracted, core-rich) basis sets.
• Comparison of convergence rates and accuracy for core properties and valence excitations (ionization potentials, electron affinities).

Main Results:

• Previous underestimation of binding energies was attributed to insufficient basis set convergence.
• Standard basis sets (cc-pVnZ, def2-nZVP) exhibit contraction errors, leading to unreliable extrapolations.
• Uncontracted basis sets and specialized core-rich families (pcSseg-n, pcJ-n, ccX-nZ) show significantly improved and faster convergence.
• Specialized basis sets maintain accuracy for valence excitations, comparable to aug-cc-pVnZ.

Conclusions:

• Basis set convergence is crucial for accurate GW calculations of core-level binding energies.
• Specialized basis sets offer a superior cost-accuracy ratio for simulating molecular spectra.
• These basis sets provide a balanced description of both core and valence electronic properties.