  Given an element in the first homology of a rational homology 3-sphere $Y$,
one can consider the minimal rational genus of all knots in this homology
class. This defines a function $\Theta$ on $H_1(Y;\mathbb Z)$, which was
introduced by Turaev as an analogue of Thurston norm. We will give a lower
bound for this function using the correction terms in Heegaard Floer homology.
As a corollary, we show that Floer simple knots in L-spaces are genus
minimizers in their homology classes, hence answer questions of Turaev and
Rasmussen about genus minimizers in lens spaces.
