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Coupled cluster treatments of periodic systems from strongly localized reference functions: 1‐D and 2‐D spin and electron lattices
Author(s) -
Miguel Beatriz,
Cousy Maixent,
Malrieu JeanPaul
Publication year - 1998
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/(sici)1097-461x(1998)67:2<115::aid-qua6>3.0.co;2-y
Subject(s) - hamiltonian (control theory) , coupled cluster , degenerate energy levels , delocalized electron , wave function , ground state , quantum mechanics , physics , heisenberg model , cluster expansion , chemistry , condensed matter physics , molecule , mathematics , mathematical optimization , ferromagnetism
A modified coupled cluster method is applied to the research of the ground‐state energy of periodic systems described by model Hamiltonians. The reference function is always a strongly localized function. The method is applied first to Heisenberg Hamiltonians and spin‐frustrated one‐dimensional (1‐D) chain and square lattices, starting from Neel functions or from products of bond singlets. The same method is then applied to Hubbard Hamiltonian for 1‐D chain and two‐dimensional (2‐D) square lattices starting from Neel function or products of bond molecular orbitals (MOs). In both cases the wave operators involve a very limited number of local operators. Despite its simplicity, the method is able to treat quite satisfactorily highly degenerate situations, approaching correctly the highly delocalized regime from the Neel function or the highly correlated regime from a product of bond MOs. However, the method is not precise enough to treat the subtle phenomenon of bond alternation of polyacetylene. The coupled cluster method from strongly localized reference functions represents an elegant and quite efficient exploratory tool, but its accuracy is limited by the poor treatment of collective effects. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 115–132, 1998