Thed-dimensional softcore Coulomb potential and the generalized confluent Heun equation

Abstract

An analysis of the generalized confluent Heun equation (α2r 2 + α1r) y ′′ + (β2r 2 + β1r + β0) y ′ − (ε1r + ε0) y = 0 in d-dimensional space, where {αi, βi, εi} are real parameters, is presented. With the aid of these general results, the quasi exact solvability of the Schrödinger eigen problem generated by the softcore Coulomb potential V (r) = −e 2 Z (r + b), b > 0, is explicitly resolved. Necessary and sufficient conditions for polynomial solvability are given. A three-term recurrence relation is provided to generate the coefficients of polynomial solutions explicitly. We prove that these polynomial solutions are sources of finite sequences of orthogonal polynomials. Properties such as recurrence relations, Christoffel-Darboux formulas, and the moments of the weight function are discussed. We also reveal a factorization property of these polynomials which permits the construction of other interesting related sequences of orthogonal polynomials.