where y = 1 1 + exp ⁡ ⁡ ( r − − R a ) , μ μ = i γ γ 2 − − ν ν 2 , 2 m E ℏ ℏ 2 = − − ν ν 2 , ν ν < 0 and 2 m V 0 ℏ ℏ 2 a 2 = γ γ 2 . Here 2 F 1 ( a , b ; c ; z ) = ∑ ∑ n = 0 ∞ ∞ ( a ) n ( b ) n ( c ) n z n n ! is the hypergeometric function.