Backup.

src/Models/TransverseIsing2D.jl

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+struct TransverseIsing2D <: SpinHalf
+    parameters::Dict{String,Any}
+    sites::vector{Index{Int64}}
+
+    TransverseIsing2D(Lx::Int64, Ly::Int64) = new(
+        Dict{String,Any}(
+            "Lx" => Lx,
+            "Ly" => Ly,
+            "J" => 1.0,
+            "hx" => 1.0,
+            "hz" => 0.5,
+            "pbc" => false,
+        ),
+        siteinds("S=1/2", Lx * Ly)
+    )
+end
+
+function getHamiltonian(model::TransverseIsing2D)::MPO
+    ampo = OpSum()
+
+    Lx = model.parameters["Lx"]
+    Ly = model.parameters["Ly"]
+    J = model.parameters["J"]
+    hx = model.parameters["hx"]
+    hy = model.parameters["hy"]
+
+    lattice = square_lattice(Lx, Ly; yperiodic=false)
+    for b in lattice
+        ampo += -4.0 * J
+    end
+
+end