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Spin‐optimized resonating Hartree‐Fock configuration interaction
Author(s) -
Takeda Ryo,
Yamanaka Shusuke,
Yamaguchi Kizashi
Publication year - 2007
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.21495
Subject(s) - spin (aerodynamics) , configuration interaction , hartree–fock method , ultra high frequency , space (punctuation) , projection (relational algebra) , chemistry , cover (algebra) , fock space , symmetry (geometry) , atomic physics , physics , computational chemistry , quantum mechanics , algorithm , computer science , mathematics , molecule , thermodynamics , engineering , mechanical engineering , telecommunications , operating system , geometry
The resonating Hartree‐Fock Configuration Interaction (Res HF‐CI) method is an efficient tool to investigate complicated strongly correlated systems such as ion‐radical systems. In this method, we explore several spin‐unrestricted Hartree‐Fock (UHF) solutions that are energetically low‐lying. However it is difficult to choose the symmetry‐broken references appropriately as the site increases. In this study, we present the spin‐optimized procedure, which is based on the Löwdin spin‐projection method, for the Res HF‐CI theory, denoted as SO Res‐HF CI. We apply this SO Res‐HF CI method to depict the potential curves of typical polyradical systems and compared the computational results using complete‐active‐space (CAS) CI based on UHF natural orbital (UNO), spin‐projected UHF, and the previous version of Res HF‐CI. We discuss the relation between computational results and the electronic configurations that are important to cover the electron correlation effects for each system. Further, we apply SO Res‐HF CI method for the simple organic radical. In addition, we extend this scheme to the GHF case, and show that the use of GHF as a seed of SO Res‐HF CI is desirable for the spin‐frustrated systems. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007