Articles you may be interested inA comparison between the Mo/ller-Plesset and Green's function perturbative approaches to the calculation of the correlation energy in the manyelectron problem J. Chem. Phys. 93, 5826 (1990); 10.1063/1.459578 Unitarygroup approach (UGA) to the configuration interaction (CI) problems of the manyelectron systems. II. Weyl graphical method of twobody operator matrix elements J. Chem. Phys. 89, 3079 (1988); 10.1063/1.454964 Parastatistics and the Clifford algebra unitary group approach to the manyelectron correlation problem Unitarygroup approach (UGA) to the configuration interaction (CI) problems of the manyelectron systems: A graphical formula in terms of Young tableausUnitary. group ap~roach (UGA) to the many-electron correlation problem is generalized by eI?beddmg the unttary group l!(n) in a .much larger group U(2n) via the rotation groups SO(m) wIth m = 2n or 2n + 1 and thelr covenng group Spin (m). Exploiting the spinorial Clifford algebra basis associated with Spin (m), it is shown that an arbitrary N-electron configuration state can be repr~sented as a linear combination of two-box Weyl tableaux ofU(2 n ), and the explicit representatlOn for Urn) generators as simple linear combinations ofU(2n) generators is given. The problem ofU(n) generator matrix element evaluation for two-column irreducible representations then red~ces to an elementary p.roblem of evaluation of generator matrix elements for the totally symmetnc two-box representatlOn ofU(2n). Thus a general N-electron problem is effectively reduced to a number of t\~o-boso~ problems. The proposed formalism also enables us to exploit other than Gelfand-Tsethn couphng schemes and particle nonconserving operators.

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Symmetry adaptation of spin-free multishell electron configurations in molecules to general non-Abelian point groups has been carried out. Using the basis spanning'the irreducible representation [2N/Z--S, 12S, on-NIZ-S ] of the unitary group U ( n ) as primitives, the Wigner operators for point groups were applied to generate the required basis. In the process it was found that the segments of the Weyl tableaux could be handled individually. Using this and the matric algebra of permutation group a viable procedure has been developed for point groups adaptation. A program based on the procedure has been generated and implemented.