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cQTP25: A new exchange-correlation functional for core-electron ionization energy.

Rodrigo A Mendes1, Nathanael J King2, Alex Brown2

  • 1Quantum Theory Project, University of Florida, Gainesville, Florida 32611, USA.

The Journal of Chemical Physics
|November 12, 2025
PubMed
Summary
This summary is machine-generated.

We developed a new exchange-correlation functional, cQTP25, for improved core-electron ionization energy predictions using x-ray photoelectron spectroscopy. This functional shows strong performance within Koopmans's framework, enhancing Density Functional Theory accuracy.

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Area of Science:

  • Computational Chemistry
  • Quantum Chemistry
  • Materials Science

Background:

  • Accurate prediction of core-electron ionization energies is crucial for interpreting X-ray photoelectron spectroscopy (XPS) data.
  • Existing exchange-correlation (XC) functionals in Density Functional Theory (DFT) have limitations in precisely modeling these core electronic properties.

Purpose of the Study:

  • To introduce and evaluate a novel XC functional, cQTP25, specifically designed to enhance the accuracy of core-electron ionization energy predictions.
  • To benchmark cQTP25 against various established XC functionals across different levels of theory.

Main Methods:

  • Development of the cQTP25 functional, optimizing range-separation parameters by focusing on core 1s electrons.
  • Benchmarking using the Koopmans's theorem approximation (IP1s = -ɛ1s) and the ΔDFT method for core ionization potentials.
  • Inclusion of both non-relativistic and relativistic corrections in all calculations.

Main Results:

  • Within Koopmans's framework, Quantum Theory Project (QTP) functionals, particularly cQTP25, demonstrated superior performance.
  • The ΔDFT method revealed that M11, ωB97X, and BHandHLYP functionals were more accurate than cQTP25, which ranked fourth.

Conclusions:

  • The cQTP25 functional offers a significant improvement for core-electron ionization energy predictions under the Koopmans's approximation.
  • Further investigation using the ΔDFT method is recommended for a comprehensive understanding of functional performance across different theoretical frameworks.