Phase diagram of the frustrated spin-1/2 Heisenberg antiferromagnet in 2 dimensions

Using a Lanczos technique we study the frustrated spin-(1/2 Heisenberg model on square lattices of 16 and 20 sites. Frustration is introduced by an interaction along the diagonals of the plaquettes with coupling $J_2$≥0. For large $J_2$ we found that the ground state breaks (spontaneously) the lattice rotational symmetry. For intermediate values of $J_2$, the squares of order parameters associated with spin-Peierls and ‘‘twisted’’ states have a peak while a similar quantity for a chiral state shows no interesting structure.