MARSHALL-PEIERLS SIGN RULE FOR EXCITED-STATES OF THE FRUSTRATED J(1)-J(2) HEISENBERG-ANTIFERROMAGNET

We present analytical and numerical calculations for some exited state s of the frustrated J(1)-J(2) spin-1/2 Heisenberg model for linear cha ins and square lattices. We consider the lowest eigenstates the subspa ces determined by the eigenvalue M of the spin operator S-total(z). Be cause of the reduced number of Ising basis states in the subspaces wit h higher M we are able to diagonalize systems with up to N = 144 spins . We find evidence that the Marshall-Peierls sign rule survives for a relatively large frustration parameter J(2).