Critical theory of the topological quantum phase transition in a spin-2 chain

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We systematically study the phase diagram of S=2 spin chain, by means of density-matrix renormalization group and exact diagonalization methods and confirm the presence of a dimer phase in the AKLT--SZH model. We find that the whole phase boundary between the dimer and SZH phases, including the multicritical point, is a critical line with the same central charge c=5/2. Finally, we propose and confirm that this line can be described by the SO(5)₁ Wess-Zumino-Witten (WZW) conformal field theory.