Matrix H in Subspace 83 with Dimension 4

H is the Hamiltonian. Here we set µ=0. For grand-canonical calculations add -6µ to the main diagonal.
U -2*Sqrt[2]*t 0 0
-2*Sqrt[2]*t U -2*t 0
0 -2*t U -2*Sqrt[2]*t
0 0 -2*Sqrt[2]*t 0