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

2*(h + U)	0	(-I)*Sqrt[6]*t
0	2*(h + U)	((3 + I*Sqrt[3])*t)/2
I*Sqrt[6]*t	((3 - I*Sqrt[3])*t)/2	2*(h + U)