H is the Hamiltonian. Here we set µ=0. For grand-canonical calculations add -6µ to the main diagonal.

4*h + U	(-I/2)*(-3*I + Sqrt[3])*t	0
(I/2)*(3*I + Sqrt[3])*t	4*h + U	((3 + I*Sqrt[3])*t)/Sqrt[2]
0	((3 - I*Sqrt[3])*t)/Sqrt[2]	4*h