SYMMETRICAL-GROUP-BASED METHODS IN QUANTUM-CHEMISTRY

The eigenvalue problem of a Hamiltonian represented in a finite-dimens ional model space being the N-electron subspace of the 2K-spinorbital Pock space is analyzed. It is pointed out that the permutation group S N is a very convenient framework for this analysis. The resulting appr oach is known as the symmetric group approach to the N-electron proble m. Its applications to construction of a basis in the model space, to the evaluation of matrix elements of spin-independent and of spin-depe ndent operators and, finally, to solution of the eigenvalue problem of the Hamiltonian are briefly reviewed. Recently developed applications of the symmetric group to studies of the Heisenberg Hamiltonian spect ra and to evaluation of spectral density distribution moments are also dicussed.