so finding a basis of low-energy states amounts to finding all tuples { k n } obeying e ( k ) ≤ ≤ Λ Λ . Let's denote all such states schematically as | i ⟩ ⟩ . Next, the matrix elements V i j can be computed explicitly using the canonical commutation relations. Finally, the explicit Hamiltonian H ( Λ Λ ) i j = e i δ δ i j + g V i j has to be diagonalized.