Chapuisat, X., Nauts, A., & Deharengdao, D. (1983). Adiabatic-to-diabatic Electronic State Transformation and Curvilinear Nuclear Coordinates for Molecular-systems. Chemical Physics Letters, 95(2), 139-143. https://doi.org/10.1016/0009-2614(83)85083-0 (Original work published 1983)