Two-Dimensional Tensor Product Variational Formulation
  We propose a numerical self-consistent method for 3D classical lattice models, which optimizes the variational state written as two-dimensional product of tensors. The variational partition function is calculated by the corner transfer matrix renormalization group (CTMRG), which is a variant of the density matrix renormalization group (DMRG). Numerical efficiency of the method is observed via its application to the 3D Ising model. 
Tomotoshi Nishino, Yasuhiro Hieida, Kouichi Okunishi, Nobuya Maeshima,   Yasuhiro Akutsu, and Andrej Gendiar