Symmetric group approach to spin-dependent CI

A general algorithm of configuration interaction (CI) method for spin-depen dent Hamiltonians in a basis of spin-adapted N-electron configuration state functions is formulated. The method is derived from the symmetric group ap proach (SGA) to a many-electron problem and retains the simple structure of the spin-independent CL The transition from an algorithm for a spin-indepe ndent Hamiltonian to a general spin-dependent case results in a replacement of the blocks of irreducible representation matrices of the symmetric grou p (representing permutation operators in the spin-adapted N-electron basis) by larger matrices representing the pertinent spin operators. The structur e of the algorithm, in particular the set of loops in the orbital graph lea ding to non-zero contributions to the CI matrix elements, remains exactly t he same as in the spin-independent case. (C) 2001 Elsevier Science B.V. All rights reserved.