中文摘要：

采用精确对角化方法,研究自旋1/2一维J1-J2海森堡自旋链模型的相变问题.通过计算激发态下自旋格点群的约化忠实度和冯·诺依曼熵,确定了该系统由自旋液体态到二聚态之间的K-T相变,并通过外推法,确定相变点位置L→∞,λc=0.241 14.研究结果表明,难以用传统序参量来刻画的K-T相变可以用自旋格点群（子系统）的约化忠实度和冯·诺依曼熵来反映.

英文摘要：

In this paper, exact diagonalization（ED） method is used to investigate the quantum phase transition in one-dimension spin 1/2 J1-J2 Heisenberg model. Through the calculation of reduced fidelity and von Neumann entro- py of spin cluster in the excited states of the model, the phase transition point of Kosterlitz-Thouless transition（K-T） is determined between spin fluid and dimerized phase in the system, and its theoretical value L→∞,λc=0. 241 14 in the phase transition point are drawn by extrapolation. The results suggest that, K-T phase transition, elusive to be characterized through traditional order parameter, is accessible by using these two calculation methods of reduced fi- delity and von Neumann entropy of spin cluster（subsystem）.