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| Main Authors: | , , , |
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| Format: | Preprint |
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2026
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2605.29924 |
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| _version_ | 1866916061278896128 |
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| author | Casida, Mark E Ponra, Abraham Munyuki, Gadzikano Natarajan, Bharathi |
| author_facet | Casida, Mark E Ponra, Abraham Munyuki, Gadzikano Natarajan, Bharathi |
| contents | Ideal density-functional approximations (DFAs) should account for dynamic, static, and nondynamic correlation. While common DFAs struggle with the latter two, the Ziegler-Rauk-Baerends-Daul multiplet sum method (MSM) provides a pragmatic way to include static correlation. In this article, we use diagrammatic MSM density-functional theory (diag MSM DFT) using the two-orbital two-electron model (TOTEM) to extend MSM DFT to include nondynamic correlation without relying on symmetry arguments. Building on previous formulations [A. Ponra, C. Bakasa, A.J. Etindele,and M.E. Casida, J. Chem. Phys. 159, 244306 (2023); M.E. Casida, A. Ponra, C. Bakasa, and A.J.Etindele, J. Chem. Phys. 162, 144317 (2025)] that lacked relaxation effects, this article incorporates relaxation via nonorthogonal configuration interaction (NOCI). We demonstrate that this modified diag MSM DFT produces an accurate ground-state potential energy curve (PEC) for lithium hydride (LiH), even at the ionic-to-open-shell-singlet avoided crossing characterized by significant charge transfer. This encouraging result suggests that the model can be extended to (at least) other singly and multiply-bonded diatomic molecules, while providing insight into a novel way to include strong correlation in DFT. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_29924 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Diagrammatic Multiplet-Sum Method (MSM) Density-Functional Theory(DFT): III. Inclusion of Relaxation and Application to LiH Casida, Mark E Ponra, Abraham Munyuki, Gadzikano Natarajan, Bharathi Chemical Physics Ideal density-functional approximations (DFAs) should account for dynamic, static, and nondynamic correlation. While common DFAs struggle with the latter two, the Ziegler-Rauk-Baerends-Daul multiplet sum method (MSM) provides a pragmatic way to include static correlation. In this article, we use diagrammatic MSM density-functional theory (diag MSM DFT) using the two-orbital two-electron model (TOTEM) to extend MSM DFT to include nondynamic correlation without relying on symmetry arguments. Building on previous formulations [A. Ponra, C. Bakasa, A.J. Etindele,and M.E. Casida, J. Chem. Phys. 159, 244306 (2023); M.E. Casida, A. Ponra, C. Bakasa, and A.J.Etindele, J. Chem. Phys. 162, 144317 (2025)] that lacked relaxation effects, this article incorporates relaxation via nonorthogonal configuration interaction (NOCI). We demonstrate that this modified diag MSM DFT produces an accurate ground-state potential energy curve (PEC) for lithium hydride (LiH), even at the ionic-to-open-shell-singlet avoided crossing characterized by significant charge transfer. This encouraging result suggests that the model can be extended to (at least) other singly and multiply-bonded diatomic molecules, while providing insight into a novel way to include strong correlation in DFT. |
| title | Diagrammatic Multiplet-Sum Method (MSM) Density-Functional Theory(DFT): III. Inclusion of Relaxation and Application to LiH |
| topic | Chemical Physics |
| url | https://arxiv.org/abs/2605.29924 |