Your spells can pierce wards against negative energy and even affect undead targets.
For example, you could cast a thanatopic vampiric touch or enervation spell on a target under the effects of death ward, and the target would suffer the normal effect of the spell. Saving throws and SR (if any) still apply. Undead are susceptible to spells augmented by this feat, as it retunes the negative energy to be harmful to them. A thanatopic spell that would kill a living creature (such as by giving it negative levels equal to its Hit Dice) destroys an undead (though undead such as ghosts, liches, and vampires may reform as normal). Undead affected by thanatopic spells that give negative levels automatically make their saving throws to remove negative levels after 24 hours.
Level Increase: +2 (a thanatopic spell uses up a spell slot two levels higher than the spell’s actual level.)
Pathfinder Roleplaying Game Ultimate Magic. © 2011, Paizo Publishing, LLC; Authors: Jason Bulmahn, Tim Hitchcock, Colin McComb, Rob McCreary, Jason Nelson, Stephen Radney-MacFarland, Sean K Reynolds, Owen K.C. Stephens, and Russ Taylor.