A parallel plate capacitor of capacitance $$12.5$$ pF is charged by a battery connected between its plates to potential difference of $$12.0$$ V. The battery is now disconnected and a dielectric slab ($$\epsilon_r = 6$$) is inserted between the plates. The change in its potential energy after inserting the dielectric slab is _____ $$ 10^{-12}$$ J.