Diagonal Curvature in Second Order Jahn Teller Theory Can Be Negative: An Analytic Proof with First-Principles Confirmation in NH3

Zhian Li, Hanxiang Mi, Xiyue Cheng +2

We demonstrate that the diagonal curvature in second-order Jahn-Teller theory (SOJTT) can be negative, invalidating its foundational positivity assumption. Using a frozen-phonon ma…