Let $X$ be a smooth, projective rational surface and $Z$ be a zero-dimensional subscheme of $X$. Denote by $\mathcal{I}_Z$ the ideal sheaf of $Z$ in $X$ and $\mathcal{O}_Z$ the structure sheaf. Is it true that $$\mbox{Hom}_X(\mathcal{I}_Z,\mathcal{O}_Z) \cong \mbox{Ext}^1_X(\mathcal{I}_Z, \mathcal{I}_Z)?$$ Any hint or reference will be most welcome.