K and with i 1 ≥ 0, i 2 ≥ 0 and i 3 ≥ 0. Furthermore, Since the potential is symmetric with respect to ∆Q 3 , only the even values of i 3 are possible. L V K is a parameter which controls the number of terms or functions in the expansion. More precisely, for each value of K, R K is defined as follows: