Jost function for singular potentials

An exact method for direct calculation of the jest function and Jest soluti ons for a repulsive singular potential is presented. Within this method the Schrodinger equation is replaced by an equivalent system of linear first-o rder differential equations, which after complex rotation, can easily be so lved numerically. The Jest function can be obtained to any desired accuracy for all complex momenta of physical interest, including the spectral point s corresponding to bound and resonant states. The method can also be used i n the complex angular-momentum plane to calculate the Regge trajectories. T he effectiveness of the method is demonstrated using the Lennard-Jones (12, 6) potential. The spectral properties of the realistic interatomic He-4-He- 4 potentials HFDHE2 and HFD-B of Aziz et al. [Mol. Phys. 61, 1487 (1987)] a re also investigated.