SYMMETRICAL-GROUP APPROACH TO THE STUDIES OF SPIN-1 2 LATTICES/

A technique for studying spin-1/2 lattices, based on the properties of the symmetric group S-N, is presented. It is shown that the symmetric -group approach, applied to the Heisenberg Hamiltonian, leads to effic ient diagonalization algorithms. Some examples of calculations for the lowest singlet and triplet states of the 2XL isotropic antiferromagne tic Heisenberg ladders are compared with results in the literature. Fo r the singlet-triplet gap we have obtained, by extrapolation to the bu lk limit, the values 0.498 949 and 0.499 545 for a polynomial and an e xponential fit, respectively.