Second Renormalization of Tensor-Network States

We propose a second renormalization group method to handle the tensor-network states or models. This method dramatically reduces the truncation error of the tensor renormalization group. It allows physical quantities of classical tensor- network models or tensor-network ground states of quantum systems to be accurately and efficiently determined. References: [1] H.C. Jiang, Z.Y. Weng, T. Xiang, Phys. Rev. Lett. 101, 090603 (2008). [2] Z. Y. Xie, H. C. Jiang, Q. N. Chen, Z. Y. Weng, T. Xiang, Phys. Rev. Lett. 103, 160601 (2009).