Entanglement Properties of the Harmonic Chain
  We study the entanglement properties of a closed chain of harmonic oscillators that are coupled via a translationally invariant Hamiltonian, where the coupling acts only on the position operators. We consider the ground state and thermal states of this system, which are Gaussian states. The entanglement properties of these states can be completely characterized analytically when one uses the logarithmic negativity as a measure of entanglement. 
K. Audenaert, J. Eisert, M.B. Plenio, R.F. Werner