Lower bound of Schr{\"o}dinger operators on Riemannian manifolds

We show that a weighted manifold which admits a relative Faber Krahn inequality admits the Fefferman Phong inequality V $\psi$, $\psi$ $\le$ CV $\psi$ 2 , with the constant depending on a Morrey norm of V , and we deduce from it a condition for a L 2 Hardy inequality to holds, as well as conditions for Schr{"o}dinger operators to be positive. We also obtain an estimate on the bottom of the spectrum for Schr{"o}dinger operators.