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New perspectives on unitary coupled‐cluster theory
Author(s) -
Taube Andrew G.,
Bartlett Rodney J.
Publication year - 2006
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.21198
Subject(s) - unitary state , propagator , coupled cluster , wave function , exponential function , mathematics , quantum mechanics , mathematical physics , physics , algebra over a field , pure mathematics , mathematical analysis , molecule , political science , law
The advantages and possibilities of a unitary coupled‐cluster (CC) theory are examined. It is shown that using a unitary parameterization of the wave function guarantees agreement between a sum‐over‐states polarization propagator and response theory calculation of properties of arbitrary order, as opposed to the case in conventional CC theory. Then, using the Zassenhaus expansion for noncommuting exponential operators, explicit diagrams for an extensive and variational method based on unitary CC theory are derived. Possible extensions to the approximations developed are discussed as well. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006