Within the tensor network framework. the (positive) thermal density operator can be approximated by a double layer of infinite Projected Entangled Pair Operator (iPEPO) coupled via ancilla degrees of freedom. To investigate the thermal properties of the spin-1/2 Heisenberg model on the square lattice. we introduce a family of fully spin-$SU(2)$ and lattice-$C_{4v}$ symmetric on-site t... https://www.knowall.blog/