Entanglement used to identify critical systems

We promote use of the geometric entropy formula derived by Holzhey et al. from conformal field theory, S_l~(c/3)log(sin\pi l/N), to identify critical regions in zero temperature 1D quantum systems. The method is demonstrated on a class of one-dimensional XY and XYZ spin-1/2 chains, where the critical regions and their correponding central charges can be reproduced with quite modest computational efforts.