Vibrational eigenvalues are computed using the Fourier-grid Hamiltonian (FGH) method with 501 grid points. FGH has periodic boundary conditions, so a padding interval, equal in width to the data set, is added to the left and right sides of the potential to suppress periodic artifacts. Each padding interval is filled with a constant (flat) potential defined by its nearest computed value. To test for periodicity artifacts, the unsigned sum of wavefunction amplitudes at the left and right edges is divided by the maximum amplitude. If that ratio exceeds 10 -6 , the padding interval is increased. The high-resolution, low-level potential is interpolated using cubic splines to yield the function g(R).