The d-dimensional softcore Coulomb potential and the generalized confluent Heun equation

An analysis of the generalized confluent Heun equation (alpha(2)r(2) + alpha(1)r) y " + (beta(2)r(2) + beta(1)r + beta(0)) y' -(epsilon(1)r +0(epsilon)) y = 0 in d-dimensional space, where {alpha(i), beta(i), epsilon(i)} are real parameters, is presented. With the aid of these general results, the quasi-exact solvability of the Schrodinger eigenproblem 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 the recurrence relations, Christoffel-Darboux formulas, and 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. Published by AIP Publishing.