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Symmetry breaking in spin‐restricted, open‐shell Hartree–Fock wave functions
Author(s) -
Li Xiangzhu,
Paldus Josef
Publication year - 2009
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.22098
Subject(s) - open shell , hartree–fock method , quantum mechanics , physics , intermolecular force , molecule , formalism (music) , symmetry (geometry) , unitary state , fock space , coupled cluster , chemistry , mathematical physics , geometry , mathematics , art , musical , political science , law , visual arts
Relying on a unitary group approach (UGA) to coupled‐cluster (CC) theory for open‐shell systems we formulate a spin‐free analogue of Thouless' theorem and derive stability conditions for spin‐restricted, open‐shell Hartree–Fock (ROHF) solutions. The formalism is illustrated on the ground states of the oxygen and boron molecules. For the O 2 molecule, the broken‐space‐symmetry solution appears already for a slightly stretched OO bond. For the B 2 molecule we find a broken‐symmetry solution even at the equilibrium geometry and, in fact, in almost an entire region of intermolecular separations. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009