Maximal inequalities and Riesz transform estimates on L^p spaces for Schr\"odinger operators with nonnegative potentials

We show various $L^p$ estimates for Schr\"odinger operators $-\Delta+V$ on $\RR^n$ and their square roots. We assume reverse H\"older estimates on the potential, and improve some results of Shen \cite{Sh1}. Our main tools are improved Fefferman-Phong inequalities and reverse H\"older estimates for weak solutions of $-\Delta+V$ and their gradients.