Fluctuations of collective coordinates and convexity theorems for energy surfaces

Constrained energy minimizations of a many-body Hamiltonian return energy landscapes e(b) where b=<B> representes the average value(s) of one (or several) collective operator(s), B, in an "optimized" trial state Phi_b, and e = <H> is the average value of the Hamiltonian in this state Phi_b. It is natural to consider the uncertainty, Delta e, given that Phi_b usually belongs to a restricted set of trial states. However, we demonstrate that the uncertainty, Delta b, must also be considered, acknowledging corrections to theoretical models. We also find a link between fluctuations of collective coordinates and convexity properties of energy surfaces.