Density functional theory with fractional orbital occupations

2012/01/31 by Jeng-Da Chai, Jeng‐Da Chai · 2 citations
Chemistry · Materials Science · Physics and Astronomy · #Ab initio #Advanced Chemical Physics Studies #Atomic physics #Bond-dissociation energy #Chemistry #Computational chemistry #Density functional theory #Excited state #Formalism (music) #Fullerene Chemistry and Applications #Local-density approximation #Machine Learning in Materials Science #Molecular physics #Molecule #Physics #Quantum mechanics #Singlet state #Time-dependent density functional theory #cond-mat.mtrl-sci #physics.chem-ph #physics.comp-ph #quant-ph

paper · pdf · doi:10.1063/1.3703894

published as J. Chem. Phys. 136, 154104 (2012) · accepted for publication in J. Chem. Phys., 45 pages, 21 figures, 3 tables, supplementary material not included

arxiv created 2012/04/01 · openalex publication_date 2012/04/17 · arxiv updated 2015/06/03 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05

Abstract

In contrast to the original Kohn-Sham (KS) formalism, we propose a density functional theory (DFT) with fractional orbital occupations for the study of ground states of many-electron systems, wherein strong static correlation is shown to be described. Even at the simplest level represented by the local density approximation (LDA), our resulting DFT-LDA is shown to improve upon KS-LDA for multi-reference systems, such as dissociation of H(2) and N(2), and twisted ethylene, while performing similar to KS-LDA for single-reference systems, such as reaction energies and equilibrium geometries. Because of its computational efficiency (similar to KS-LDA), this DFT-LDA is applied to the study of the singlet-triplet energy gaps (ST gaps) of acenes, which are "challenging problems" for conventional electronic structure methods due to the presence of strong static correlation effects. Our calculated ST gaps are in good agreement with the existing experimental and high-level ab initio data. The ST gaps are shown to decrease monotonically with the increase of chain length, and become vanishingly small (within 0.1 kcal/mol) in the limit of an infinitely large polyacene. In addition, based on our calculated active orbital occupation numbers, the ground states for large acenes are shown to be polyradical singlets.

Citations

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Cited by

• Thermally-assisted-occupation density functional theory with generalized-gradient approximations
• Role of exact exchange in thermally-assisted-occupation density functional theory: A proposal of new hybrid schemes