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Quasispin symmetry for the derivation of coupled cluster equations for the Hubbard model of benzene
Author(s) -
Vinette F.
Publication year - 1992
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.560420611
Subject(s) - hamiltonian (control theory) , hubbard model , homogeneous space , physics , algebraic number , symmetry (geometry) , mathematical physics , computation , cluster (spacecraft) , quantum mechanics , mathematics , computer science , geometry , mathematical analysis , mathematical optimization , superconductivity , programming language , algorithm
The concept of quasispin is applied to a special case of the Pariser–Parr–Pople ( PPP ) model of the benzene molecule, namely, the Hubbard Hamiltonian. Added to the spin, space, and alternancy symmetries already taken into account in the PPP Hamiltonian, this new symmetry, called quasispin symmetry, has the effect of reducing the size of the CI matrix. Coupled cluster ( CC ) equations are then obtained after applying the CC approach with doubles as well as its extension that accounts for triexcited clusters ( CCSDT ‐1). The derivation of these equations following the use of quasispin to the Hubbard model of benzene constitutes the most simple nontrivial example of CC results. In addition, the CC equations can be written in explicit algebraic form using the symbolic computation language MAPLE.