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Fractional occupation numbers and spin density functional calculations of degenerate systems
Author(s) -
Takeda R.,
Yamanaka S.,
Yamaguchi K.
Publication year - 2003
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.10359
Subject(s) - degenerate energy levels , complete active space , atomic orbital , interpolation (computer graphics) , ab initio , spin (aerodynamics) , space (punctuation) , density functional theory , ethylene , chemistry , computational chemistry , molecule , quantum mechanics , physics , molecular orbital , thermodynamics , computer science , classical mechanics , organic chemistry , motion (physics) , catalysis , electron , operating system
We implemented ab initio self‐consistent field (SCF) fractional occupation numbers (FON) calculation with Dunlap's interpolation scheme for the twisted ethylene, which is a prototype molecule of a σ–π biradical system. The calculational results are compared with those of complete‐active‐space (CAS) SCF and spin‐unrestricted Kohn–Sham (UKS) calculations on potential surfaces, occupation numbers of natural orbitals, and correlation entropies. It was found that the UKS methods gave similar results to CASSCF, while the FON solutions appeared in only the nearly complete degenerate region. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 317–323, 2003