Demonstration of how the Kohn variational method works for electron-potential scattering

Ref: McCurdy, C. W., Rescigno, T. N., & Schneider, B. I. (1987). Interrelation between variational principles for scattering amplitudes and generalizedr-matrix theory. Physical Review A, 36(5), 2061–2066. https://doi.org/10.1103/physreva.36.2061

The Kohn method is a application of the variational principle for solving general few-body scattering problems. In other words, KohnVar is a template for solving a 1-D electron-nucleus scattering for an arbitrary potential, arbitraray electron energy, and arbitrary basis functions.