Diagrammatic multiplet-sum method (MSM) density-functional theory (DFT). III. Inclusion of relaxation and application
Mark E Casida1, Abraham Ponra2,3, Gadzikano Munyuki4
1Laboratoire de Spectrométrie, Interactions et Chimie Théorique (SITh), Département de Chimie Moléculaire (DCM, UMR CNRS/UGA 5250), Institut de Chimie Moléculaire de Grenoble (ICMG, FR2607), Université Grenoble Alpes (UGA) 301 rue de la Chimie, BP 53, F-38041 Grenoble Cedex 9, France.
The Journal of Chemical Physics
|July 10, 2026
Summary
This study introduces a modified diagrammatic multiplet sum method density-functional theory (diag MSM DFT) to include nondynamic correlation. The enhanced method accurately models potential energy curves, offering a new approach for strong correlation in density-functional theory.
Area of Science:
- Quantum Chemistry
- Computational Chemistry
- Density-Functional Theory
Background:
- Standard density-functional approximations (DFAs) often fail to capture static and nondynamic correlation.
- The Ziegler-Rauk-Baerends-Daul multiplet sum method (MSM) offers a practical approach for static correlation.
- Previous formulations of diagrammatic MSM DFT lacked relaxation effects.
Purpose of the Study:
- To extend MSM DFT to incorporate nondynamic correlation without symmetry assumptions.
- To introduce relaxation effects into diagrammatic MSM DFT.
- To develop a more accurate computational method for systems with strong electron correlation.
Main Methods:
- Utilized a two-orbital, two-electron model for diagrammatic MSM DFT.
- Incorporated relaxation effects using nonorthogonal configuration interaction.
- Applied the modified method to study the ground-state potential energy curve of lithium hydride.
Main Results:
- The modified diag MSM DFT accurately reproduced the ground-state potential energy curve of lithium hydride.
- The method successfully handled the ionic-to-open-shell-singlet avoided crossing with significant charge transfer.
- Demonstrated the inclusion of nondynamic correlation and relaxation effects.
Conclusions:
- The developed diag MSM DFT provides an accurate and novel approach for including strong correlation in electronic structure calculations.
- The method shows promise for extension to various diatomic molecules.
- Offers valuable insights into treating nondynamic correlation within DFT.
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