Matrix H in Subspace 23 with Dimension 4

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