Abelian-symmetric Kagome iPEPSΒΆ

Specialized class for abelian-symmetric iPEPS on Kagome lattice, where sites s0,s1,s2 on down-triangles are fused together:

       |/      |/
      s1      s1
     / |     / |                  |               |
    /  |    /  |                  |/(s0,s1,s2)    |/(s0,s1,s2)
    --s0--s2--s0--s2--   =>     --a---------------a--
       | /     | /                |               |
       |/      |/                 |               |
      s1      s1                  |               |
     / |     / |                  |               |
    /  |    /  |                  |/(s0,s1,s2)    |/(s0,s1,s2)
--s2--s0--s2--s0--s2--          --a---------------a--
       | /     | /                |               |
       |/      |/
      s1      s1
      /|      /|

The resulting tensor network is defined on a square lattice in terms of rank-5 on-site tensors. Physical index runs over the product of Hilbert spaces of s0,s1,s2 in this order. These Hilbert spaces are assumed to be identical.