Orthogonally-spin-adapted coupled-cluster theory for closed-shell systems including triexcited clusters
The orthogonally-spin-adapted form of the nonlinear system of equations for the extended coupled-pair many-electron theory, which involves the monoexcited, biexcited, and triexcited states and cluster components, is derived. A diagrammatic approach, based on second quantization, the time-independent Wick theorem, and the graphical methods of spin algebras, is employed. The advantages of using the orthogonally-spin-adapted states and cluster components, rather than the nonorthogonally-spin-adapted ones which have been previously employed, particularly in the triexcited case, are also discussed. It is also shown that the formulas for the direct configuration-interaction method can easily be obtained in compact form from the linear part of the system of extended coupled-pair equations.
- Research Organization:
- Quantum Theory Group, Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
- OSTI ID:
- 6092299
- Journal Information:
- Phys. Rev., A; (United States), Vol. 20:1
- Country of Publication:
- United States
- Language:
- English
Similar Records
Full coupled cluster singles, doubles and triples model for the description of electron correlation
Non-orthogonal spin-adaptation of coupled cluster methods: A new implementation of methods including quadruple excitations