Schematic view of the solutions for the one-variable (E) polynomial Eq. (7) with (a) g = 0.5, U = 0.5, r = 0.5; (b) g = 1, U = 0.5, r = 0.5; (c) g = 0.5, U = 0.5, r = 2; and (d) g = 0.5, U = −0.5, r = 0.5. Even parity is denoted by blue and odd parity by red. The black circles are numerical ED solutions for the energy. Δ = 0.5.