The concurrence is a quantity that allows us to measure the entanglement of a quantum system and can be calculated from the reduced density matrix. In this paper we show explicitly how to calculate the concurrence for a finite chain of spins s =1/2 described by the anisotropic Heisenberg model. We show that for finite chains the concurrence has a maximum at the critical point Δ = 1, which is the main feature in the thermodynamic limit. We observe that it is possible to obtain information about quantum phase transitions of the model by calculating the concurrence for chains of at least 12 sites
concurrence; quantum entanglement; Heisenberg model
