| Abstract: | A particularly compact form of the orthogonally spin-adapted coupled-cluster equations involving all singly and doubly excited clusters is derived for the general case of a non-Hartree–Fock closed-shell reference determinant. The diagrammatic approach based on the graphical methods of spin algebras is applied. The relationship of different diagrammatic procedures for spin-adaptation, employing both bare and spin-adapted two-electron interaction vertices, is discussed. A comparison with the results obtained with algebraic spin-adaption approaches is also given. |
