No, Eigenvalues[H] is not broken, but buyer beware: https://arxiv.org/pdf/1809.08178.pdf S.M. Blinder's Mathematica solution of the Ammonia problem appears to suffer from "junk in, junk out", despite him having a canonical business address on the title page. One, the references seem to be out of date, and with too old data. Two, why choose a quartic potential? While "proof" checking, I compared quartic and sextic potentials. The sextic worked much better for extracting the barrier height from ground state splitting / first excitation. Generally I am interested in Blinder's demonstrations at: https://demonstrations.wolfram.com/author.html?author=S.+M.+Blinder Unfortunately, his tutorial on Ammonia appears to me, not right enough. Would anyone second this opinion, or is there dissent from my dissent? --Brad